Yep! She understands when she’s going to the toilet and often tells us, but then refuses to have her nappy changed!
I started by putting my son on the toilet before bath/bed time then added nap times, then added before and after meal times. It wasn't long before my son was telling me he wanted to go but we haven't got the hang of poos yet only wees. Advice is to start around 18mo, check the Eric website for tips and advice x
Are they showing signs of readiness? If so I would set aside a week where you can stay home and just focus on that, it’s surprising how quickly they pick it up when they get into it. 18 months is quite young though, with my eldest nursery told me most of the children start after 2 and some are closer to 3 x