Since you're staying at Sand$ do a REEF survey with BD&A. One of the naturalists will accompany you on the dive pointing out the different fish for you to record. You pay them but it's pretty minimal. It's also your BMP orientation dive site if you're diving with them. Then dive the site yourself later, it's a simple easy entry/exit and dive and the #1 site in the Caribbean for species diversity. We found interesting things there in less than 30' of water, 100 yards from the dive dock.
Another thing you'll find off Bonaire is that the water is so clear usually that as you're swimming back to your entry point, you typically see the mooring ball rope from about 50' away. Just don't touch it, especially in the south, it's typically covered in fire coral.
Salt Pier would be a good beginner dive also. There's a tiny sandy beach there that makes the entry easy, you have to do it with a DM now, and the pier structures start in under 20' of water with several of them under 50'. We found the best stuff at the 2nd pier and didn't exceed 30' there.
Another thing you can do is dive from the various resorts. Just about every dive resort is situated on a named dive site and all have docks with flat wide steps down into the water. Being beginners you shouldn't do any diving south of Pink Beach, the currents past there can be tricky.