Unable to get gears in

The most common cause is something called "clutch drag", a condition where the clutch does not fully release and continues to (partially) transfer power to the transmission. If you're suffering from clutch drag, you will find that gears engage easily when the engine is off, but you have trouble engaging it when the engine is running. You may also find that if you start the engine while it is in gear, a small amount of "shudder" is felt even while the clutch is depressed.

It could be as simple as too much clutch play. If I recall golfs have a cable clutch, so adjustment is done under the hood where the cable connects to the clutch arm on the bell housing. On hydraulic setups it is adjusted on the clutch pedal itself.

It is also possible that the splines on which the clutch plate rides are worn, causing the clutch plate to "rub" against the pressure plate/fly wheel and not fully release because of that.

I had a similar problem on my Toyota Corolla. Adjusting clutch play improved mattes, but the problem only went way after I had the clutch replaced.

I think it comes down to adjusting your clutch play (on the Corolla the clutch play should be between 7 and 15mm, I expect others to be similar) and if that fails, to have an expert look at it. Replacing a clutch is a fairly invasive (and expensive) operation, on most front wheel drive cars it involves removing the wheels, popping the suspension joints, removing the CV joints and the transmission to get at it, so it is usually a good idea to replace everything while you're at it.