Unfortunately, most of the people on this forum are not very familiar with Family RP communities. Here is how it works....
You go to the adoption agency of your choice, pay for the parents panel and fill out the application, dropping your photo (make sure it is family friendly) and application notecard into the panel.
Next, you go and review the kids panels, when you find one(s) that you like, you will hit the "LIKE" button...if that child "likes" your panel as well, you are matched and you go on trial for a week or so. Either of you end the trail at any time.
If the trial goes well and you decide to proceed the adoption will be finalized and you can get and adoption certificate.
As far as allowance and what not....keep in mind that being a parent IS a big responsibility, you need to (at the very least) be sure that you have a home large enough to accomadate your new family, provide lots of interactive, rp experiences, you'll have to deal with school, find thea doctor , etc. It IS a big responsibility, but it is also very fun and rewarding and there is a HUGE Family RP community out there to give you lots of family things to do.
There are also options if you choose to have a baby as an introduction to the family life, again you will have to find a doctor and all the things you will need for the pregnancy and then once your prim baby arrives you will have to care for it, buy the diapers and clothes etc. just as one would expect for a new addition.