Most of these acrylic tanks are made from a single piece of acrylic molded to form a single tank like those cheap plastic tanks. The rest are joined at the seams with a type of sealant that is safe for use in aquariums. Silicone is not recommended for long term bonding. I would advise you to use Google to get an idea of what type of sealant is safe to use. Read this to have a rough idea on what to do:
You might be able to find instructional videos on acrylic tank repair on Youtube.