GET (read) examples can be run directly from this documentation. It is just a matter of clicking a link. Most browsers display the output on the same page (or another tab if you right click and select that option). Internet Explorer will probably treat the output as if you wanted to download a file. In that case just elect to open the output in a text editor.
If you want to check out the POST, PUT and DELETE (update) examples a good approach is to take a moment to install a REST plugin for your browser e.g. RESTClient for FireFox
The REST plugins will allow you to
Select the "Verb" (e.g. POST)
Enter the resource name (e.g. offices)
Add a header to indicate you are sending JSON data as part of the request body (Content-Type: application/json)
Add a header to indicate your 'tenant' (X-Mifos-Platform-TenantId: default)
Paste the example JSON into a Request Body
Send the Request (and receive a Response)