My son started to hold hid head up pretty straight at 2.5 months fully at 4 months. He started to hold toys that were put in his hand at 4 months. Hes 5 months now and is always reaching for toys. He loves to be on his tummy he kicks his legs strong and pushes himself up high.
Usually this starts at about 2-3 months, barely picking their head, up grabbing at things, etc. Then about 4-5 months they start lifting head up high, trying to crawl, grabbing things, etc. As for as the actual crawling the baby may not crawl at all. I knew a kid that never crawled. He went straight from scooting to walking early. Your baby will do it on thing at its right time.
i had alot of these questions too... i signed up to babycenter.com you put it your childs age and it sends you a news letter everyweek for your child (also when your pregnant) and tells you what should be going on around that time. it's very interesting!