Hi and welcome to the Planet.
as said above Ni is nickel, Ti is titanium, SS is stainless steel.
NI & Ti must be used in TC mode only
SS can be used in wattage and TC modes
wattage for a beginner is the way to go. a lot of kits offer all these options but there are a few tanks especially newer ones that only have wattage (kanthal) coils.
in the last 6 months we are seeing the rebirth of Mesh coils as well which are for wattage mode a well.
ive tried TC a couple of times and after almost 4 years i still only use wattage.
each coil will show the range on the side of the coil or on the box. if you get stuck just ask.
always prime a new coil by dripping juice on all the holes around the coil and a couple down the top. start on a much lower wattage than you vape at to let it bed in and turn up slowly.