Q: Car slips when trying to accelerate.

What you are describing sounds like potentially a worn out clutch. As you know, the clutch transmits engine power to the gearbox, and allows transmission to be interrupted while a gear is selected to move off from a stationary position, or when gears are changed while the car is moving. Most cars use a friction clutch operated either by fluid (hydraulic) or by a cable. When a car is moving under power, the clutch is engaged. A pressure plate bolted to the flywheel exerts constant force, by use of a diaphragm spring, on the friction plate. The drive or friction plate runs on a splined input shaft, through which the power is transmitted to the gearbox. The plate has friction linings, similar to brake linings, on both its faces. This allows the drive to be taken up smoothly when the clutch is engaged. When the clutch is disengaged (pedal depressed), an arm pushes a release bearing against the center of the diaphragm spring which releases the clamping pressure. The outer part of the pressure plate, which has a large friction surface, then no longer clamps the drive/friction plate to the flywheel, so the transmission of power is interrupted and gears can be changed. This is the process that allows you to shift smoothly through the gears. When these plates begin to wear out, as they commonly do over time, you may experience a bit of a slipping feeling when shifting from gear to gear or when accelerating from a stop. I would recommend having an expert from YourMechanic come to your location to inspect and diagnose your clutch.