2 Days ago i bought a 1991 Civic Sedan LX. I did normal tune up and everything yesterday.

This morning on the way to work . The car just locked up and skid to a stop. Its stuck in gear. Clutch works fine. Just stuck in 3rd gear i believe. I can wiggle the shifter around like its in neautral but its in gear. idk what it is.

Someone said maybe the linkage. I need help asap please.

 

Locked up means it can't roll. If you were in a gear then it would roll, but might stall your engine depending on the gear.
If it locked up and will not roll, then it would seem that gears in your trans are stuck and can not rotate.

 

its stuck in gear. i think its in 3rd. I can still drive but in that one gear and i can not put it in neatral.

 

Sounds like linkage to me too.
Get under your car and start your inspection.
I would start at the "bitch pin" and make sure it is in place - the one in this image is hanging half way out. some people put a screw in there instead of the pin (because they have baby hands and it's just too much work for their weak bodies) and those can vibrate loose and fall out.



The stabilizer bar mounts to the trans right next to it so it's easy to inspect to make sure it is hooked up. You can see it in the image above with the yellow mark on it.

Then make sure the shaft on the trans moves in and out when you actuate the gear selector in the car.

 

I'd like to know what trans that is, and why there is a gasket between the halves.