Hi, it depends on what qualifications you have already got. I got good GCSE's but failed my A levels, then went on to do an archaeology degree. Decided to have a complete change and did the GTP (Graduate Teacher Programme) which takes a year, and was awarded QTS in december. If you have a degree you could also do a PGCE which involves placements and more time in college/ university but only takes a year.
As for finding a job at the end, there are always lots of positions coming up, it's just a matter of finding one that is suitable for you, ie, year, location, school etc. Don't just go for the first job that comes up.
hope this helps.