1996 Chevy Corsica 1)my car shakes at 40mph/2) turn signals

Shaking is most likely cause by wear and tear on the vehciles suspension. A simple alignment at a local shop will usually cure this. Could be caused by worn wheel bearings or ball joints as well, which alignment shop can tell you if this is the case.

For the turn signals, it sounds like your multi-function switch (switch that turns signals on) could be faulty. Check for power going to the switch. If power is there, switch needs replacing.