1995 Ford Contour Transmission slipping

Start with basics
check the fluid level, and fluid quality when fluid is hot with engine idling. Some discoloration and darkening is normal as the fluid ages, but if the ATF is brown or has a burnt smell, it is badly oxidized and needs to be changed. Varnish on the dipstick is another indication of worn out fluid.
Because fluid level and quality can cause slippage.
If the fluid level and quality is satisfactory, the nest guess will be a slipping torque converter.
If there is engine light, please try to get the code(s)

Fluid can leak out of the driveshaft seals, the input shaft seal, the transmission pan gasket, the torque converter or the ATF cooler and line connections. If the fluid level gets low, the transmission may be slow to engage when it is shifted into drive. Gear shifts may be sloppy or delayed, or the transmission may slip between shifts. If the fluid level is really low, the transmission may cause the vehicle to not go at all.