Edited: I got confused, nevermind it's fixed now! :)

ローラさんは アメリカの りゅう学生で、いま 二十才です。 で is one of the ways of saying "and". So basically the sentence means "Lola is a foreign student from America and is currently twenty years old." で has many meanings including "at", like Nancie-san mentioned above. Since there are many ways of saying and in Japanese (you will come across し、と if you haven't already) so it may be confusing at first. Other examples would be : • この部屋はきれいで静かで、とても好きです。- That room is clean and quiet and I like it very much. • この教室は小さくて*、ここには教師がいる。- That classroom is small and there is a professor in there. I hope this helps you! EDIT : *since I am not sure you noticed my comment I will just write it down here as well. で is not used with i-adjectives (and I only realized my mistake a bit after I posted the answer), only with nouns and adjectives with no i ending. So I changed the ending of the second sentence but left it there anyway, though I think you got it now, right? However, just another way of saying and! :P Compared to English, Japanese really has a bunch of them.

If Rola was an American, and a foreign student, and 20 years old, and not married, and your cousin, you can say "ローラさんはアメリカ人で留学生で20歳(はたち)で独身で私のいとこです". If you say " ローラさんはアメリカ人です。留学生です…", of course we can figure out what you want to say. But feel something roundabout.