Best age to start?

[Amelia2012]

My daughter be 2 end of this month she has a potty already but won't sit on it she used to sit on toilet with me holding her and she done a wee and I praised her and she was happy then started crying but she won't go on toilet again now this is my first baby and I just need some advice please :)

Lots of people start potty training around this age - it works for some but not all.
I'd wait for your DD to show clear signs that she understands that she is wet/dirty etc.
Have potties in the house and encourage her to sit on them at times, such as bathtime, when the nappy is off anyway, but don't expect too much.
Profuse, over the top praise when anything happens is also good.
Don't fret if she seems later than others, my DD was 3.5 yrs old (I tried at 2 but it was a dismal failure!) they all get there in the end.