I see the slight heat variations left by your body in air left by the temperature in your body i and see a larger heat source which is your body and also see the chakra signatures. that you leave and the main ones inside you. i see all this via my sharingan of course.
While it is correct that the sharingan can pick up heat signatures, but if you have paid attention, you would know that each and every shinobi has their own chakra signature. You with the gift of the sharingan can see this unique chakra signature and memorize it as there is only one kind. So when you saw me with your sharingan it should of been easy to track me, but you insist on tracking me through heat. That is why the forrest thing didn't work, there are too many animals for you to track me through just 2T sharingan.
Now lets talk about the things that the sharingan can and can not see through. You can't see through a dense forrest. The sharingan won't allow you to do this. You are not a hyuga you are a uchiha. Which means you can't even see people through the ground, only
shallow portion of the ground you can see.
Also your sharingan precieves motion. The moment I left you could of said you seen me make a move to go a certain direction. These are all clues you could of gotten on your own and with a little research found. Either way I hope you understand now what a sharingan can and cannot due.
This is important portion of the trainnig because that is the core ability of the sharingan at the levels of 1T-3T. As the cannon sharingan techniques are very limited, you have to use it's main abilty. Let me ask you again what is the main abilities of the sharingan in your point of view?