The only recognised qualification in Tiling is an
NVQ (or SVQ) here in the UK. This can be time consuming to gain and it's only really required at the moment on commercial sites and most of those seem to be not asking for them. Although that's a bit of a grey area.
Most go on a short course and practise on their friends and family jobs and get a feel for it and start getting the right tools etc and make sure they enjoy it and feel they are capable full-time then start to either find employment or go self-employed at which point you will know if you need a
NVQ and should you feel you do, you can get one via OSAT which will be explained to you on a course at most training centres.