Learn Swedish: Det finns vatten överallt framför fontänen. - There is water everywhere in front of the fountain.

Det finns is the standard Swedish way to say "there is" or "there are" when stating that something exists. It literally translates to "it is found". If you used Där är, you would be physically pointing out a specific location, as in "Over there is water."

How can I easily remember the word överallt?

It helps to break it down! överallt is a combination of över (over) and allt (all or everything). Put together, "over all" means "everywhere" in Swedish.

Is framför a single preposition?

Yes, framför means "in front of". Even though it translates to three words in English, it is just one word in Swedish. It is closely related to the word fram (forward).

Why is the word fontänen used here instead of just fontän?

Because the sentence talks about a specific fountain: "in front of the fountain". The word fontän is an en-word, so to make it definite, you add the suffix -en to the end, resulting in fontänen.