"Prague is full of tourists in the summer."
Translation:Praha je v létě plná turistů.
Je would like to be the second word.
V létě je Praha plná turistů. or Praha je v létě plná turistů.
Not in this case, where it is a form of the verb "být" ('to be'). Keep in mind that Czech is, despite its many quirks, mostly an S-V-O language, so let's not move the verb around too much.