When to use 我是 vs 我在
Yes.

是 (verb) means "is, am, are, to be, yes" while 在 (verb) means "at, to be in, to exist", or is a short form of 正在 (adverb,) which is used to indicate an action in progress. 是 is the confirmation of a state of being, whereas 在 is a confirmation of a location, or indicates that you are in the middle of/in the process of doing something.


  是 (verb) + noun


So when you want to use "I am [x]" where [x] could be a student/a teacher/an old man/a young girl/a lawyer, that's when you use 是. What comes after it is a noun.

e.g. 我是留学生。你是哪国人？她是我女朋友。


  在 (verb) + place name


Where you want to use "I am at [x]" where [x] is a place like Beijing/America/etc., that's when you use 在. What comes after it is a place name.

e.g. 我在北京学习汉语。你在哪儿？他在美国旅行。


  正在/正/在 (adverb) + verb


When you want to indicate a continuing action "I am currently [x]" where [x] is a verb like reading a book/watching TV/cooking dinner, you use 正在/正/在. What comes after it is a verb.

e.g. 我正在看电视。你在想什么？她正做饭。