I'm a total noob in this camera field. I want to buy one so if you'd kindly tell me what those things(aperture, sensor size, lens) mean in a camera's specification and what to look for while buying one, I'd really appreciate it
If you do want to get into DSLRs and photography as a long-term interest/hobby, I would strongly recommend putting much more of your budget into lenses rather than a camera body. I good 10 year old lens is still a good lens today, whereas a 10yr old camera body is basically worthless. So good quality lenses will last you much longer, and can be kept for multiple body upgrades. A good lens on an older/cheaper SLR will also produce much, much nicer images (in most situations) than a cheap lens on a top end camera. So again... divert as much of your budget to lenses as you can.
You need to research though. Figure out what you equipment will suit your needs. If you go into a store, unless you have a massive budget they'll sell you the latest body and a range of kit-lenses. While that's okay, essentially there's nothing you can build on, because the body will age quickly and the lenses just aren't that great. Often you're better picking up a second hand body and one nice quality lens which suits your needs (telephoto for wildlife for example, or a portrait lens if that's more your thing). At least then you have something decent that will last you a long time.