I have a 97 miata w/ 5 speed. When I push in the

Sounds like the clutch needs bled.

can be a normal situation as the teeth ends hit each other and will not mesh
not noticed if the engine is running as the teeth are moving
have you seen the clutch lever moving or are you just assuming it is good
probably didn't/doesn't need a clutch but a clutch master cylinder

The transmission has synchronisers to help line up the gears when you shift from one gear to another. If this transmission has been treated rough or rawhided and speed shifted, these synchroniser clips become bent and turn up and won't allow the synchroniser to slid over them into place and hold the transmission in gear. Eventually you will have to replace them. You will notice if you take it easy when shifting, it will get easier. Don't get in a hurry and jam the shifter or it will just get worse and they will have to be replaced. I hope you better understand how your shifter work. I hope you can buy some time before you have to put a fair amount of money it to it.
Good Luck.

With engine off, does the shifter get gears easily?
If so, it could be your hydraulic clutch. Check the fluid level on the clutch master cylinder's reservoir-on the firewall. If it is low, add brake fluid to it. If it was dry, you will probably have to bleed the hydraulic clutch down at the slave cylinder on the transmission bell housing.
When clutch pedal is pressed, the clutch master cylinder will force fluid down the line to the small slave cylinder. There, a small plunger is forced out (about an inch or less) from the slave cylinder, and pushes the clutch fork forward. The fork causes the clutch inside the bell housing to operate. Look for this movement of the slave cylinder pushing the clutch fork while someone presses down or pumps the clutch pedal. With the engine off, of course.

If the shift linkage is not binding on the outside of the transaxle, then something inside like a shift fork has broken. The transaxle will have to be removed for repair. Such is the way with 20 year old cars where old things break, bad luck for you. It will be an expensive repair. An alternative is a used 5 speed from a salvager. That and a new clutch could have you going again in short order.

Why was the clutch replaced in the fist place? will it go into gear with the engine off? if so, the shifter and linkage is ok. what happens if you put it in gear, and then crank the truck, it it tries to go, then the clutch is not releasing. how does the pedal feel? Spongy? normal? If it feels spongy and the slave is new, replace the master and bleed the air out, until it feels normal, like its pushing on the clutch

The one item I would suspect is the through-out-bearing not completely disengaging the pressure plate from the fly wheel. If the vehicle is in neutral and you slowly depress the clutch and release it do hear a singing or whining sound? Since you cannot adjust the clutch any more the through-out-bearing is the component which moves the pressure plate from the fly wheel to stop the power from the engine to the transmission. It is difficult to shift when the engine is on because the fly wheel is still engaged and powering your transmission.

Hi:
The shift pattern is pretty much the same on all 5 speed cars. The top row is the odd numbers, 1-3-5
the bottom row is 2-4-Reverse. The center position is neutral

Here is the key: The shifter is slightly spring-loaded to the center position. If you hold in the clutch pedal and pull the shifter to neutral, and let go of it, it will automatically be lined up in the position, that if you pushed it forward , it would go to 3rd gear, and if you pulled it back, it would go into 4th gear.
This way, to start driving, you start out in neutral, grab the shifter lightly, and push it first to the left, then forward. This is first gear, where you start out. when you want to shift to second, push in the clutch, and keeping left pressure on the shifter, pull all the way back . Here is the easy part, 2nd to 3rd. When you are ready, push in the clutch, and just push the gear shift forward , till it hits neutral, and is spring loaded to the middle. Then you just push it straight forward to 3rd, then next shift, straight back to 4th.
Last gear, 5th: push forward to the neutral row, then Push to the right till it lines up ,and forward to the 5th gear. Reverse should only be shifted into from a dead stop. Find neutral, push the shifter all the way right, then pull back towards you. Hope this helps.
Practice a bunch in the driveway!

manual?? put it in first gear --hold foot on clutch and start engine ,car will shoot forewards but do not be deterred drive car with foot on clutch and after a short distance the clutch will clear and the engine will rev up ,now release the clutch and drive as normal ,it will be ok from now on

Do you mean: The transmission goes into gear but the car does not move? Is somebody in the habit of coasting the car down hills with the clutch in so they don't have to shift? Coasting down a hill with the transmission in a low gear can cause the clutch disc to spin so fast that centrifugal force throws the lining off the disc. I blew up my clutch man! If this is the case you need a clutch job to learn an expensive lesson. Or starting out in second or third gear and slipping the clutch to get the car going. Just as bad just as expensive! Most have been told not to slip the clutch, Not all have been told not to coast in gear. If you like to coast put the transmission in neutral and let the clutch out. If this is not the case then the clutch is hanging up internally, put the car in gear and let is set over night. Can you push it with the clutch up? You shouldn't be able to. Now push the clutch down and let it up. If you can push the car now it is hanging up (sticking) internally. The clutch master/slave hydraulic system needs looked at.