You know, it is wise to post questions AFTER you have at least tried to study.

There are THOUSANDS of patterns when to and when not to use this, but as an quick intro for you, let me show you some possible patterns. They are NOT COMPLETELY PRECISE RULES, but they will serve as a stepping stone to further learning. [DO] * When you find your Japanese sentence you've created ends with any noun (but if the noun expresses some action, you'd better use "します" instead of this) [DON'T] * When you find your Japanese sentence you've created ends with any verb the last character of which is "す" or "る" (ex. You should avoid "ますです" or "するです". The former should be "ます", the latter should be "します" ) After you get the rule above in place, you might want to look in some grammar references in website or printed book so that you can learn more about that.

We use "～です（desu）"　when we talk with elder people. We shouldn't better use it when we talk with our friends.

To be honest, you can find numerous results by googling with keywords "japanese desu grammar" or "japanese desu how to use" or whatever, since your question is one of the most basic and common question of Japanese. It's also nice to know that google is for free.

I'll go to Syria as a part of countries in my trip. Do you have recommendable place in Syria? I hope you tell me.