I don't know if it's ready...need help

This is my first time making a belgian strong and my first time with plans for two stage fermentation.

The fermentation has been going for 11 days with the airlock bubbling every 5seconds or so. I decided to check the gravity which read 1.019. The OG was 1.070.

How do I know when it's done fermenting? Also, if it is not done fermenting, can I still rack to the secondary fermentation?

After I checked the specific gravity, and put the cover and airlock back on, no more bubbling. That's weird.

So I guess my questions are:

Is secondary fermentation for actual fermentation or "conditioning", and if just conditioning, by racking when primary is not complete, do I risk ruining it?

Also, how do I know it's done fermenting? Do I simply check the SG every day or two to see if it is constant and not going down?

Lastly, on a side note, how do you know if it has become infected? I'm always nervous about that.

Can you tell I'm a newbie?

Thanks.

A secondary is mostly used for clearing/conditioning, not fermentation (unless using two yeast strains, but that's another story.) Yes, you know it's done when the readings are the same for several days. But, I would still urge you to just leave the beer in the primary for 3-4 weeks more and then transfer to the seconday. Many don't even bother to secondary, but if you choose to, there is no need to rush. Especially with a Belgian strong, you need a lot of patience. And that patience will be rewarded!