Also, saying Danios does not really tell us which fish you mean as there are about 26 species of danio in the genus. Some can work in a 10 gal. tank while others cannot. Here is a site which will illustrate what I mean http://www.fishbase.org/identification/SpeciesList.php?genus=Danio
New hobbyists have little experience and knowledge built up yet so choosing fish can be daunting experience. I can tell you how I approached things 16 years ago when I was setting up my first tank. I started by looking at pictures of fish on the internet and in the Baensch Aquarium Atlas vol 1. Whenever I saw a fish whose look appealed to me, I would try to research the fish to determine a few things:
1. Could it thrive in my tap water?
2. Could it cohabit with the other fish I had found I planned to or did keep?
3. Was my tank the proper size for that fish?
4. Could I give it proper care and meet its needs for its entire life?
If I could not answer the above questions with a well reasoned yes, I would not get it. Despite all this care, I have still made mistakes. Bear in mind that this hobby is no different than any else new with which we get involved. There is a learning curve. There is nothing wrong with learning from our mistakes when we have made a good effort to try and avoid avoid them by trying to learn as much as we can first. You are already doing this in your post as you are tying to learn before you act.
I have always tried to read on three sites as the first step to learn about a fish:
This site has good info on many species.
The SeriouslyFish.com site.
The Mongabay.com site.
What I suggest that has worked for me is to use Google. I will enter the "Latin name of the fish" + the site name. It will often work with the common name, but common names may generate some confusion. Here are examples of how to get information for Zebra Danios aka Danio rerio on Google:
"Danio rerio + Seriously" or "zebra danio + badmans" or if you are not certain of the exact species "Danio + mongabay" This last format would get you to a site's page for the genus from which you can then select the species. All three sites may not have info on a given fish and they may also not be in 100% agreement on some things. But for the most part they are pretty accurate.