Youtube - you don't have to pay anything.
Learning yoga can become tedious, to be honest. Unless you have already tried it before and liked it a lot you will most likely not be able to finish as traditional yoga is usually about 1+ hours.
There are easier/funner ways to do yoga that work even better than the traditional. Its all about trying new things out like the upward cradle, which even though you won't be able to get it right at first its entertaining to do and it works way better than traditional yoga moves.
I learned a lot of yoga exercises and poses from watching videos on YouTube.
There are also many blogs which teach Yoga poses. Use any search engine to find them. A good article to learn about Kripalu yoga is here : http://info37.info/what-is-kripalu-yoga/
Good luck ! Yoga is a great choice !
Why bother about paying money when it’s all free on YouTube!? You simply need
to look for videos that demonstrate beginner techniques and view them as many
times as you want to master the art. You will definitely find tons of content
on the site, give it a go and all the best!