If you are looking to test IE which is only available on the PC, but you only have a Mac, you will need to download a virtual machine, load the windows operating system and go from there.
If you are on a PC, but wish to see what things look like in a browser on a Mac, they are likely to look the same as long as you have the same browser (either mac or PC version should technically produce the same results).
You can download Safari on PC. Firefox will look the same on Mac and PC. IE... you can only download a really old IE for Mac that is no longer being used.
If you still want modern IE on your mac, you should download a virtual machine and load up a Windows OS into it; it will run in a separate window. This requires an Intel-based mac. A virtual machine comes with the PC-based OS preinstalled.