On my 89 LX-i Transmission...
To check the level of the manual transmission, you will have to get under the car, but make sure you raise it completely level. There should be two bolts, a fill/inspection bolt (higher of the two) and a drain bolt (lower on the tranny). Open the fill/inspection bolt and put your finger inside the tranny and feel for the oil level. If the level is not right under the hole, you aare low on fluid. Fill the tranny with good quality engine oil (10W-30 or 10W-40) through the same hole that you have open(yes, you will need a funnel and some rubber tubing).
If the level is low, you may consider draining the entire tranny and replacing all of the fluid, instead of mixing old and new oil. To drain, simply open the lower bolt (the drain bolt) and allow all of the oil to drain out. Then replace the drain bolt, and fill as mentioned above.
Hope this helps.