Need any advice I can get please

I have recently entered a relationship with a girl I have had a thing for since high school. But since high school she has been with someone else until a couple of months ago and in that time she has had a child with him, (a little boy) and he is now just over 19 months old so I'm coming into everything quite late on. This is the first time that I have been in a situation where I've been looking after a young child, being a bit of a kid at heart myself I can get on well with children but that's usually when they're walking and talking and have been for several years but I've never even had a younger brother or sister to help look after as my younger sister is only 2 years younger than me and there's never been any call for me to even babysit in my teens.
Really I would just like any advice I can get for helping look after him because so far my own childlike nature has helped me in getting on with him and keeping him entertained but I'm clueless in all other aspects of looking after a kid, I've even had nappy changing explained to me several times and it's still a bit confusing. Also I'm not entirely sure that it was such a great time for me to be getting involved as I've heard all the stuff about the "terrible two's" and he has already started showing some signs of what I've heard children do around this age of shouting and throwing things etc.
So again any advice for looking after him and maybe some advice on what to expect and how to deal with the behavior changes that are to come?

hi there i hav a daughter who is 18 months and my son is three they r bolth very different in most ways ive just been slowly finding you really hav 2 go with there flow of things changing a bum is not always easy i often hav 2 change my little girl standing because she dont like laying down hopefully u will find the way but really there is no wrong or right way

Hi. I experienced something very similar to what you are going through. While at university a met a girl we got on well and things moved along. Anyway it turned out she had a 6 month old kid when I met her. I was very nervous (don't want to break it) initially but soon got over it. Sounds like you're doing the right things. Nappy changing was tricky to start but gets easier as you go along. It is a difficult time to start learning this skill as the child will be moving around and able to wriggle away. Its easier to learn when they're smaller as they can't escape, so don't take it to heart if you struggle.
The child's father was and still is on the scene 10 years on, which took some getting used to on both sides, and caused a lot of tension. Grin and bear with it because the rewards are endless.