First of all, you have to have some drum/bass loops. Loops are short pre-recorded tracks that are usually 4-8 beats long, that when played over repeatedly sound like one long track. To use these in ACID Pro, the best thing to do is open the explorer and chopper window's. Use the explorer to find and insert the loop. Then use the chopper to insert the track repeatedly for the length of the song. Then you can use the tempo slider to adjust the tempo of the song.

Try that out, and if you have any more questions post them here, and I will try to go a little more in depth.