I have an 11 speed. Would someone please help me with what I need to buy to replace the worn chain. Shamino Devore

An 11-speed chain and a chain tool.

11 speed Shimano Deore? Is your Trek 7.3 FX upgraded? You will need:

A chain: Shimano XT/Ultegra CN-HG701 11-Speed Chain (competitivecyclist.com);
A bike chain pin tool: Park Tool CT-3.3 Bicycle Chain Tool : Sports & Outdoors (amazon.com); and
These excellent quick link pliers: Super B 2-in-1 Master Link Pliers (The Trident) : Sports & Outdoors (amazon.com).

A bike shop won't charge you much to put it on. Especially if you buy it from them.

Besides the correct chain and tool, you'll also need to know how to size the length of the chain. If the original is correct then break the new chain to be the same number of links.

I would say same length but the some other member will pipe up saying the new chain will need to be .5% or more shorter than the old

1. Check out this good video on chain replacement. It shows the tools needed and detailed steps of replacing a chain.

https://www.parktool.com/blog/repair...railleur-bikes

2. The video recommends matching chain and derailleur brand, but that is not necessary. Your Shimano derailleur is compatible with SRAM and KMC brand chains. I prefer these because they use a master link to connect the ends, rather than a pin. I've used both these brands with Shimano road and mountain drive trains with zero issues. (Also I like to spread the wealth amongst manufacturers.)

3. Note, towards the end of the video, if your new chain skips on the cassette as you ride and especially if you pedal hard, you may also need a new cassette. If the chain is worn such that it's elongated (or stretched), it could've worn the cassette to the elongated length, and thus the new chain won't engage into the worn cassette.

Count the pins of the chain you removed (if you pushed a pin out, count that one, also). Then lengthen the new chain so that when assembled (with either a pin or quick link) it has the same number of pins as the old chain. Leave your meter straps in the tool box.

To be fair, most Shimano chains now also come with a Quick Link, including the one I linked above.

Thanks for the correction. I've been using SRAM/ KMC for so long (>20 years), I forgot Shimano adopted the master link too,

I would like to thank everyone for there help. I cleaned the cassette and chain yesterday evening. Here is a shot of the cassette and the chain with a chain gage. If I read this right the chain is good?

Still trying to figure this out.