No one has given you a complete list of what you are going to need once you get a mech mod so here it goes:
Sony VTC batteries (there are others, but just get these for simplicity and safety)
Atty (FastTech Patriot is a good, big atty)
Mod (I'd say Copper Pegasus)
Wire (Start with 28g Kanthal)
Organic Cotton Balls
Various tools (tweezers, wire snips, mini-screwdrivers, etc)
Charger (Nitecore i4 or i2 is a decent cheap charger)
MULTIMETER or OHM READER!!! (Multimeter will also let you read battery voltage so you know when your battery is getting low, but you'll notice a drop in vapor production)
Don't let your batteries go below 3.6ish. I usually swap out at 3.7. That's what they read when I notice a change in vaping.
Mech mods turn into a hobby so be prepared to watch a lot of YouTube videos and spend more money than what you thought.