Your best bet is try with sdl2.

Here are the libs: https://www.libsdl.org/download-2.0.php

Here the api reference: https://wiki.libsdl.org/APIByCategory

and here some good starting tutorials: http://www.willusher.io/pages/sdl2/

good luck

If you want to do it a low level fashion - learning everything, check out http://www.handmadehero.org. <- best resource i know to learn game development and every aspect of them.

Also a tower defence game is not really that hard, just break it down:

You do not need any physics system at all. Just simple collision detection tests.

At start you can simply use waypoints for the creeps and move from point to point - can be easiely extended to use a proper path finding system.

Maps can be fully made with tiles, super simple to create, edit and render and can be produced with extistent tilemap editors like "TileD Map Editor".

Creep movement is just a linear interpolation between two points over time.

The only part which may be tricky (depending on your math skills) is to predict the enemies target point for the towers depending on the enemies speed - If you just use the enemies current position as a tower target you mostly will not hit the enemy (depends on the tower placement).

If you need some help, i have made a full tower defence game before, so i know how everything works - so dont hesitate to ask.

See: http://root.xenorate.com/final/towadev/0.5.1-alpha/