In Chinese actually we don‘t have ’times‘，if you want to say ’I ate a pizza yesterday‘= 昨天我吃了一个pizza. It means that you only have to add the time it happened, no matter it happened yesterday, last week, or in the future. This part of chinese is very easy, you don‘t have to think about changing anything，you just add the time，that’s it！
Another situation is that if you can't remember when it happens clearly, you add'了'or ‘过’after the verb. For example: 我看过《Avatar》我看了《Avatar》= I've watched 《Avatar》before.
我吃过饭了=我吃饭了=I've had my meal.
But when you want to express the future and not sure when, you can use '要' or ‘将要’before the verb：for example 我要去超市买牛奶=I 'm going to the supermarket to buy milk.