Most tents these days come with taped seams. That’s fine, but overtime those seams can delaminate. Many boutique tents do not come with taped seams, so you have to seal the tent at home before using it. Unless you like sleeping in a puddle. Not a cuddle puddle, just a wet, cold puddle.
Seam Grip SL Silicone Tent Sealant (also works on tarps!) is a relatively easy to apply seam sealer or resealer. Brush it on more or less as thin as you can, but push it into the nooks and crannies where multiple seams come together. The better job ya do, the drier you be.
This stuff is kinda stinky, so set up your tent in your roommates room while they are at work, and do your seam sealing in there. The tent should be pitched and taut.
Oh, I should say: don’t seam seal your inner tent, that isn’t water proof. Seal your fly, or if you have a singlewall tent, the roof of the tent. I seal the tent’s bathtub floor edges as well.
One tube is enough for one 2 person tent, if you put it on thin, as you should.