Is your fan kicking on to high speed?
Many computers get "hot" but the cases are plastic (so they blow hot air out of a vent). But the plastic case does not conduct away the heat (which isn't good) but they compensate with the stronger fan and vent. Users get the illusion that the computer isn't hot because they don't feel the heat directly.
The macs use aluminum cases because the entire case can be used to help dissipate heat. This means it is normal for it to be "warm" ... but "hot" depends on how hard the CPU cores are working. The variable speed fans normally run on low speed but will start running faster and faster as needed to help with cooling. The aluminum case cooling design means the users do feel the heat. But the design is better for cooling the machine because entire case effectively becomes one big heat-sink.
You can launch activity monitor to determine which applications or processes are using the most CPU.
My personal MacBook Pros tend to get "warm" (if using them on my desk, I use a riser that props up the back of the mac so that the bottom doesn't sit flat on the desk. This helps it cool from the bottom side of the case (specifically I use something called the "Lazy Couch" by Just-Mobile).
My work MacBook Pro... tends to run much hotter. The (mandatory) security software that my company installs is ... not great. That machine's CPUs are pegged so hard during the first 10 minutes after booting that it's basically non-responsive.
My suggestions are:
If you think your machine is hot (and apparently you do) make sure the machine is able to dump the heat through the case. This means you maximize the amount of surface area that has contact with air (especially the bottom).
Use Activity Monitor to determine which process(es) are responsible for driving the highest CPU utilization. You may have things running that don't need to run.
There are 3rd party utilities (e.g. iStat, Fanny, etc.) that will report the actual CPU temperature. You might consider installing one of them and checking the temperature.
Farther down the list:
Are your fans working? They are normally fairly quiet ... but if the machine is "hot" (really hot) then you should certainly hear the sound of the fans running at high speed. If you do not hear the fans, contact Apple for diagnostics and/or service. (E.g. computer may be running especially hot if the fans aren't working correctly)
This isn't likely if it's a newer mac ... but if older ... possibly an accumulation of dust may be responsible for poor air circulation and your mac may benefit from a cleaning.