A wheel's hardness is marked on its side. The quality of the bearings will affect the amount of effort the skater must apply to rotate the wheels. Bearings are rated according to the precision with which they are made. The difference between ABEC 1 and 5 bearings is not usually a major factor to the beginning skater. Lower priced skates will not use rated bearings.
Wheels wear out.
They must be rotated to avoid uneven wear and to get the maximum use from them. The skate you purchase should allow you to rotate and replace the wheels easily. Most manufacturers provide a maintenance guide that will explain this procedure.