again go study music theory, just the basics help.
If you make all your music in c major that's fine you can always transpose them up or down the scale all the major and minor scales are relative it's when you go into non western music thats the scale becomes advanced
here's 2 beats i made no samples, made this shyt from the ground up. but if you want to sample the key is to find the bpm, time signature, and music scale. that takes practice
Yasuke - this one i used a japanese scale, got the instruments from a kontakt bank, and made a crazy drill track
Red Lipstick Joint - simple little afro rnb join i did in d# minor