Chains are where you can get a lot of grit and just plain dirtiness accumulating so it’s something you should clean and maintain on a regular basis. If you need to install a chain, remember to get one that is compatible with your system because the larger the number of sprockets you have on your bike, the thinner the chain you will need. A thin chain for a 10-sprocket bike can theoretically be used on sprockets designed for wider chains.
The inverse is not true. You cannot use a chain from a single-speed bike (wider sprocket) on a 10-speed (thinner and multiple sprockets).
First, you’ll need to size the chain. To do that, you’ll need to click the shift levers so that the front derailleur is on the largest chainring and the rear is on the smallest sprocket. Thread the new chain over the big sprocket and chainring. You don’t need to thread it through the derailleurs just yet. Measure off where the chain meets and then count two pin-holes of extra chain links. REMEMBER: you must cut the chain so that it ends with the inner plates and not with the outer plates. If the measurement lands right on a link with outer plates, cut the chain one link up so you end up with inner plates and not outer ones. SRAM uses what they call a “power lock”, a master link that has an elongated pin-hole and is used to connect the ends of the chain.
Use your chain break tool to cut the chain and then proceed to properly thread it through your derailleurs. Now attach your power lock.
In order to tighten and set the lock, pass the chain through till you get the lock sitting right above of the chainrings. Tensing the chain with the crankarm and the back tire, this action should pull the chain enough so that the lock can set.
NOTE: The chain explanation in the video happens about halfway through but since it is SRAM, I decided to stick with this video in particular.