This is a pretty vague, general question, since there are dozens of reasons why a laptop gets hot.
Through normal usage, though, the laptop internals (CPU, GPU, RAM, etc) will get hot from being used for a while. Whatever your system uses to regulate fan speed (if there is any active cooling inside) probably keeps your laptop operating at a set temperature deemed safe.
You may want to keep the ventilation holes free from any obstructions, like dust and other objects sitting in front of it. This will allow the heat building up inside to properly exhaust.