Chain placement I need to know the proper chain route for a 21 speed mongoose

I had a look at the Mongoose website.
They have manual for download.

https://int.mongoose.com/pages/product-manuals

Enter the model of your bike, or look for a picture of it.
Follow the instructions....

REgards
Geoff

Hey, Local bike shop determined that both wheels were defective. I took the junk back to Walmart and got a refund... PROBLEM SOLVED!!

Check out https://gearly.org/ for more info.

Thanks.

Look here

http://www.manualsonline.com/

This is a complex operation requiring special tools. I suggest you take your bike to the local bike shop for proper completion.

oil the chain and get faster tires

The first thing you need to do any chain work is a chain tool
This allows you to push a pin out to break the chain and then push the pin back in to lock it and then release the pin to allow the chain to bend. One of these is a must for any rider, cheao and could save your ride if a derailleur breaks or something.

http://www.parktool.com/blog/repair-help/categories/derailleur-systems

http://www.parktool.com/blog/repair-help/chain-installation-derailleur-bikes

You haven't actually asked a question, so I am guessing that you want to know how to replace a bicycle chain on a 21 speed bike. To remove the chain you need to use a chain tool that presses one of the pins out of the one of the chain links (any link, there is no master link). To put the new chain on you use the chain tool to press the pin in. This is just a little tricky with a chain tool, but it's just about impossible without it. They sell these tools at bike shops and maybe even at Wal-mart. Take a look at this link to see a what I'm talking about. http://www.parktool.com/blog/repair-help/chain-installation-derailleur-bikes By the way, Park tools are very good quality for the money.

just change the gears.