I have been problem for learn the past and the furure
The past and the future are just points of view that human beings have from their present. But presents are multiples in accordance with the place where you stand in the universe. Kant considered time and space as a priori categories of sensibility. So dont worry!
Jokes aside, alm, I think the problem you tell us here is not an easy matter.
First of all you'll get aware that the grammar issues are coming in your workbook little by little as you are going ahead with your GG lessons. They'll stay there at your disposal anytime you want. Don't miss to visit your workbook as often as possible.
Here along the thread headed "Grammar" in this forum I think you'd better to ask some particular issues of expressing past and future. I'm sure that Silky, the best competent teacher I've ever met, will help you out of any awkward grammar matter. And she'll do it in a lovely manner, without looking at you from head to toes like do some good Samaritans when giving alms out. How lucky you are, alm!
Please, alm, read "multiple" without any s at the end. Multiple is an adjective and adjectives are uncountable in English. (At least, I think so.)