We’ll cross that bridge when we come to it is an English expression meaning that there’s no point dealing with a problem until you come across it. I think this expression is particularly valid for language learning.
There’s no point trying with all your might to understand the present perfect when you lack vocabulary, and, frankly, you’re nowhere near getting to a point when you’re going to naturally understand the present perfect. One of my students last year said he was working in an English-speaking environment and he was often unsure as to when to use the present perfect – but he said there are more important things, and he was right!
This student went to meetings with English and American people and took a notebook to remember the expressions they were coming out with. And there were not few of them, there are loads of expressions you can learn without getting caught up on a tense you might never understand. In practical English usage books, there are 3 or 4 pages on the subject (or more) but you’re not going to have time to check out those 3 or 4 pages in full-blown conversation.
So, don’t get ahead of yourselves, when you’re ready, you’ll be able to cross the bridge, but if you’re not, well, you’re not: time will tell. You can do things to prepare yourself for the journey: train yourself to make phone calls or go to meetings, but don’t expect to understand everything straightaway, you won’t! It’s too much. On top of that, it’s not really about understanding, it’s about being able to think in the language, and that’s two different things.