Learn Hardcore Arabic (Modern Standard): عند الجسر الكبير توجد ساحة، وعلى يسار الساحة مقهى صغير. - At the big bridge there is a square, and on the left of the square there is a small café.

عند الجسر الكبير توجد ساحة puts the location first: At the big bridge, there is a square.
توجد ساحة عند الجسر الكبير starts with the existence of the square: There is a square at the big bridge.

Arabic often moves location phrases to the front when setting the scene.

What does توجد mean here?

Here توجد means there is / there exists / is found.

It comes from the verb وجد in the passive/existential sense to be found, to exist. In Modern Standard Arabic, يوجد and توجد are very common for expressing there is / there are.

So:

توجد ساحة = there is a square

In English, there is just part of the structure there is. In Arabic, the idea is expressed by the verb itself.

Why is it توجد and not يوجد?

Because the subject is ساحة, and is .