Rule #1, don't import anything that's been compressed (unless it's a lossless compression like HuffYUV) ! WMM tolerates compressed footage for the most part, but Premiere will refuse.
This guide explains everything about importing, and many of the examples are for Premiere:
Once you've imported your clips to Premiere, just drag them onto the "Video 1" bar. Drag the left and right edges of the clip to trim it, or use the razor tool to cut it in half.
EDIT : Oh yeah and
"A Newbie's Guide To Adobe Premiere"