If you want to edit your build, tapclick
button right next to your build name (you can also find all your builds in your user page).
If you want to create build, tap onclick (add new) icon in bottom right corner and select class you want.
To add hero build to new deck, tapclick a little cards icon right next to build name (build doesn't have to be yours, but be aware that builds of others can be removed by them).
After that, new button should appear in bottom right corner, it will link you to deck creation page, you can add as many builds as you want. Editing deck works in same way as editing hero builds, use icon here or on your user page.