If wishes were horses then beggars would ride,
If turnips were swords I'd have one by my side.
If 'ifs' and 'ands' were pots and pans
There'd be no need for tinkers hands!
I think this means that you should concentrate on what you have rather than on what you don't have.
I think it's 'an' rather than 'and' - 'an' is an old word for 'if'; may still be in German. So it's saying that 'if' we had all we wanted we'd be fine, ie stating the obvious. Tinkers mended pots and pans so 'if' we had lots we wouldn't need to mend old ones.