How can i get more Fit?

I'm 19, don't really do alot of sports but would like to get more fit, i eat healthy, making my own dinners majority of the time, im not fat, actually im pretty skinny but wanna get tonned up a little, but i want to do in in secret to see if anyone notices, id liek to be bale to do it at home also, so far i do pressups but it doenst really seem to be doing alot :/