an 'un-learn' button?
sometimes I find that what I'm learning is getting a little to hard for me and that I need to go back and learn the basics of stuff, I thought that if other people are having the same problem we can have an 'un-learn' button next to say 'animals' or 'family' or 'food' or any block of things you learn, (of coarse it would take away the skill points you had in that section) but I think that it is very important that what we learn is very strong before we move on...becues when we get to high that we can't practice words without failing I think that means we should go back and review, Please tell me what you think
You are certainly right when you say that we have to review what we've learned. However, I don't think any "un-learning" is necessary for that. You can always go to any previous skill and redo the lessons or use "Practice skill" button. It is also a good practice to start your Duolingo time with a few practice rounds.
One may think that Duolingo should make some obligatory practice in order to make us acquire really strong knowledge before going further; but this will also make learning too boring to those who are not complete beginners and don't need so much repetition. People learn with different pace, so it is good that it is up to us to decide whether we want to learn a new lesson or to practice some old ones.
Listen to yourself and assess your achievements. You can set your own rules, for example:
Repeat the lesson until you are able to finish it with full hearts.
Repeat the lesson until you feel there are no more sentences that you have not seen yet.
After every 3 lessons, do untimed practice until you manage to finish it with full hearts. Then do timed practice until you manage to gain full 20 points for it. Only then move to the next lesson.
Start every new day with "Practice all skills" rounds and repeat them until you get 20 points for a round.
Start your work at the current skill with timed practice of lessons already learned in this skill. Don't move to new lessons if you can't gain full 20 points.
Do a timed practice round for each of two previous skills.
These are only examples. Don't be afraid to try and adjust your learning so that it would be successful and pleasant.
You can always go back and practice lessons in a skill like Olimo mentioned. Keep an eye on your word strength, and you'll be able to see which lessons you might want to practice some more.