Easy WP LaTeX provides a very easy way to display math and equations in your posts using LaTeX. Lets you customize colors and sizes of your equations.
The easiest way to install this plugin is to use the WordPress Admin interface. Go to your admin dashboard, find the "Plugins" menu, and click on "Add New". Search for this plugin and click on "Install Now" and follow the WordPress instructions.
If you want to download it and manually install, you can again use the WordPress dashboard interface. First download the plugin zip file to your local computer. Then go to your admin dashboard, find the "Plugins" menu, and click on "Add New". After clicking on the "Add New" menu item as above, click on "Upload" (below the title "Install Plugins" near the top). Browse for your downloaded zip file, upload it and activate the plugin.