Chances are she will already know about periods from friends and magazines, but, as you already know, it is really important that you help to prepare her too. Friends often think they know a lot more than they really do and come up wiht all sorts of misleading/horror stories as 'facts'. It will also help your daughter feel comfortable when she does have her first period if you bring up the topic first. My mum never told me anything about periods and was obviously hugely embarrassed about the whole topic - in fact, when I started I used to sneak pads from her stock or use my pocket money to buy my own rather than tell her I needed some
Please just be honest with her and give her facts that she can trust, talk through any worries she might have and let her know that you are comfortable with the whole thing. It will make so much difference.
As for pads/tampons, she could use tampons but they are fiddly and some girls don't feel comfortable using them, so definitely start out with pads and if she expresses interest in tampons, buy her some applicator-type ones to try. They are very useful for things like swimming and vigorous sports and some people, me included, like them as there is less mess than with pads and they can be more comfortable.
When you're buying pads, make sure they have 'wings' as they will slip around less and give better protection for your DD's clothing. She will need to change them every few hours so make sure she has enough each month (a normal-sized packet should be fine). She might also want to try pads specifically designed for use while she sleeps, as they will last through the night and are also longer so there is less likelihood of leaking and her clothes/bedsheets being marked.
Do be prepared for accidents. It is very normal for girls to have irregular cycles so she will more probably than not be taken by surprise at times. It's a good ides to encourage her to carry around a pad in a discreet pocket in her schoolbag (believe me, this is not something either of you want teenage boys discovering!) so that she isn't caught short, and possibly a spare pair of knickers as well.
I hope that helps. As she is 10, there may be a good few years before she has her first period, but she could also start tomorrow, so early preparation is essential. Good luck!