When buying a portable power planer look for:
As powerful a motor as you can afford, at least 400W is ideal.
Definite click-stopped cutting depth adjustment.
Comfortable front handle.
Fittings for a side fence.
Bevel cutting groove along the centre of the sole plate.
Generous rebate capacity - at least 18mm if possible.
Plastic drop-down toe at the rear to stop the blades damaging the workbench surface
Using a planer
As with all power tools, follow the manufacturers' safety instructions carefully.
Place the front of the plane on the end of the wood, but make sure the cutter block isn't touching the timber. Gently press down on the front handle and turn on the planer. Move the tool at an even rate along the wood. When you reach the end, transfer pressure to the rear handle and glide off the wood to avoid taking a deep gouge out of the last few millimetres of the work. Choose a portable planer than can be inverted in its own accessory stand if you want to plane a lot of small pieces.
Planing wide boards
To even out a wide surface, set the planer to its finest cut and plane diagonally to the grain, in overlapping strokes. You will still need to use a hand plane to get rid of slight machining marks. You can buy cutters with rounded off corners that do not leave heavy 'tramlines' on the surface.
Make several light passes rather than trying to take off a lot of timber in one go.