When I try to open a file, it gives me a warning that I have to have something like the above. It tells me to go to Tools but I cannot find anywhere to look for it.
To provide an answer more information is needed. Please have a look at What information should I include in a question in addition to OS and LibreOffice version? - #4 by ROSt53
Go to Menue:Tools>Options Left side you see a tree structure under LibreOffice-Advanced you will see the Java Runtime. See if it is activated.
If you don’t have one installed then you need to get one. Which one depends on your OS.