Okay so one of my friends wants me to make sounds of me stepping on wood, metal, dirt, grass, water, carpet, cardboard, leaves, gravel, mud, concrete, asphalt, glass, plastic, bullets, etc. But I'm not sure if I can synthesize that, what do I do?
The sounds (sound effects, essentially) your friend wants you to record are traditionally described as Foley Effects, and are commonly created by recording someone actually carrying out the operation, using a high quality mic and recorder in an acoustically-treated area, so devoid of any additional "noise"!
I strongly suspect that there is no way you could convincingly "synthesise" at least some of those sounds, e.g. the bullet. OTOH, it is quite possible for your friend to "buy" CDs or downloads of such sound effects. Since this is a MAGIX forum, this page on the Catooh site might be a place to start!
. . . . But he wants 50 sounds of each thing I step on, . . . .
Jeffs suggestion re CD collections is probably the best way to go - there are literally thousands of such sound effects already available in various collections from many sound effects sites on the web.
. . . . . But he wants 50 sounds of each thing I step on, I'm kind of confused on what he means . . . . .
IMHO you need clarification on what is required, then work out the costs in terms of the time and effort, and expenses you may incur to either record your own and assemble a sound effect collection or find them on the Internet.