How do I tell if I can use the Force?

You will have to find someone who is already Force Sensitive, and is willing to test you. This must be done IC.

If you ARE force-sensitive, a force user would also have to 'activate' your force powers.

(ie, Qui-Gon telling Ani that he is one with the force)

Which, Joe, they would have to test him to do, and almost certainly wouldn't bother testing him UNLESS they were going to activate him if the result is positive. I point this out only because it outlines the redundancy of your post, and that Tony already provided all the needed and relevant information.

Though a character may not even know he/she is a Force user, they gain the bonuses to their abilities automatically.

From this I assume you can tell ooc if your toon is force sensitive.
It increases your skill.
So if you are able to hire a NPC cheaper than expected based on your normal skill you are force sensitive.
If you walk faster....
If you see further with your sensor.....

See the force guide/rules which abilities are effected.

I wonder if this work correctly. Since I have no confirmation about it.

No, it does not work. The bonuses only apply when you are Force Aware.