That "little button" is the rearmost part of your recoil spring rod. Push it in and lift up the top cover, then you can remove the recoil spring and bolt carrier. There is nothing to hold the bolt back, no hold-open or anything.
Smoke is normal. Oil or cosmo or something burning away. It'll do it for a while. You really want smoke, bump fire about 4 or 5 of the 30 round mags thru it as fast as you can (hint: wear a glove on your forward hand, or hold the rifle with an oven mitt or something).
Cleaning all the oil off...ugh. Try wiping it down with a rag, actually several rags. Just keep at it. Do it outside on a warm day. Take it to the range, run some rounds thru it, and wipe it off some more. It takes a while.
Oh, and most important of all....have fun! I like the Romanian SAR's. So much so that I had to get another, an SAR-2. But I havent gotten to fire it yet, since I couldnt afford any ammo for it! Also only have one standard capacity (30 rnd.) mag, and one reduced capacity (10 rnd. It came with the rifle, I would never waste money on something so stupid!). That should change within the next couple months, though.