What is the Ram used for besides my apps.

First, you need to know that the model you have is the slowest Mac that Apple offers, a 5400 rpm hard drive and only 8 GB of RAM.

So we're starting out at a disadvantage. Let's see if there's any 3rd party software that might not be wise to have on your computer. Download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Add Text button to include the report in your reply. How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck so that it can get additional information from the Console and log files for the report:

ALSO IMPORTANT:

Then we can examine the report and see if we can optimize the performance of your iMac.

What model iMac do you have and how much RAM is installed?

While in the Activity Monitor keep an eye on the Memory pressure graph. As long as you're in the green area you're OK. Also what hard drive do you have in the iMac?

The simplest explanation is that RAM holds the operating system (the program that makes the computer run), all the programs you have launched, and any data you've loaded into the programs you are running (which includes Web sites in your browser). As I said, that's the simple explanation but it does get a bit more complex than that. In the real world we might have launched 4 programs but we can only use one of them at a time so the operating system can move data from RAM to the hard drive to free up space. This is known as virtual memory. As convenient as VM is, it has limitations so it cannot replace the need for real RAM.

The message you received means that between the operating system, the applications you were running, and the data you had loaded, the computer was no longer able to hold everything necessary in RAM and virtual memory was being used to the fullest extent possible. Two simple ways to avoid seeing this message is to limit the number of open tabs you have in your browser and to quit programs you aren't actively using.

Is your hard disk a 5400 (super slow) or 7200 rpm spinning disk? The default was the 5400 rpm which will read/write everything more than 30% slower than a 7200 rpm (which is now also considered slow compared to an SSD).

You not only need more RAM, but a better/faster hard drive. You have an entry level computer.

Or, only have one app or a browser with only 1-2 tabs open at a time. Do quit each app before opening another. Do not bother with processor intensive photo or video processing apps.

Please use the Activity Monitor app on your Mac and it will tell you all the processes that use RAM and how much at any given moment.

Your welcome, AM is in the Applications-Utilities-Activity Monitor