As a beginner you have a lot of leeway. You could do a variety of things of your choosing for a good workout, like pierini said the brisk uphill walk, a slow 30 minute jog, a fast 10 minute jog even. I usually just do whatever I'm in the mood for. If you don't feel like working out just do a quick 10-15 jog. If you've got free time, slow it down and go longer.
As far as cardio affecting lifting, not really. I've only noticed lifting affecting cardio, like when I run a timed mile after a DL or squat day. It usually doesn't interfere with lifting, even if you are
still sore.