I'm slightly overweight but want to lift for muscle gains. how to start this?

Go see your doctor: Get checked out by family doc to be sure you're otherwise healthy. Then decide if you need to pay an expensive gym membership or if you'll exercise on your own at home. You don't need expensive equipment to exercise at home either. Check out http://www.mensfitness.com/training/build-muscle/15-best-bodyweight-exercises-men & http://www.menshealth.com/fitness/body-weight-exercises-youre-doing-wrong