Upload the contents of the Mara distribution to a suitable location on your webserver. This need not be in the root of the webspace. You can do this by extracting the contents of the zip and transferring them with an FTP program such as FileZilla. Alternatively, your webhost may offer a file manager capable of uploading the zip as-supplied, and then unzipping it on the server. If available, this is the quicker method.
Open this location in a browser, and observe whether the home page (index.htm or index.php) has the top banner and lefthand menu. If so, Mara is working. Note that you must open the site through the webserver's URL. Opening the page directly as a file will not work, because this is a php site and therefore requires server interaction.
Once you have the basic page display working, add the text '?login' to the page's URL. This should cause the Mara toolbar (with a black background) to appear at the top of the page. Log in with 'admin' and 'changeme' as the default username and password. If the login is successful the bar should change to a dropdown menu.
If this the first login, you will now be prompted to change the admin password. If the installation is on a publicly-visible server, it is important to do this without delay. On the first change of the admin password the encryption salt (termed a 'site secret' in some packages) will also be changed. Its purpose is to make the login information applicable only to this site. You will then be directed to reload the page and login again, since the default account will no longer be valid.
You'll probably want to try online editing as your first action as Admin, so select Edit > Editor On from the Mara toolbar, then click anywhere in the center of the page. A floating editor toolbar should now appear. You type your changes straight into the page, and for the most part, see the effect immediately as you type.
Congratulations, installation really is as a simple as that for a basic site on an industry-standard server.
Next, you will want to create some pages of your own, and and edit the menu accordingly, so that they are offered to site visitors. You will then need to think about designing a theme for your site.
You can then delete all of the example pages (.php and/or .htm files) in the root directory with the exception of the automatic sitemap, which you should retain. Do not delete other filetypes. In Mara there is no install.php to delete post-intallation, by the way.