The Japanese word "Tatoeba" stands for "for example". That's what the page mainly consists of: Example sentences in many languages, contributed by the user community under the Creative Commons BY-License (which means that you can use them even for commercial purposes as long as you attribute the creators of the sentences). The sentences are cross-linked like a web. That way you can have e.g. an English sentence linked to its french translation which itself is linked to a Swahili sentence: indirectly you get the English-Swahili translation. That way you can have translation pairs that normally don't occur.
Also it's great to contribute, you can learn a lot by translating from one language to another.
The only bad thing that might happen to you is that you stumble upon sentences that are rude or offensive and unfortunately there is no filtering system yet.
Search example sentences translated into many languages. Add and translate your own sentences. It's collaborative, open, free, and even addictive.