In reply to a post on another topic...
Gravity Forms installs just like any other WordPress plugin.
1. download the plugin zip file to your desktop
2. go to the WordPress admin to the Plugins page and click on the "Add New" link in the left toolbar. Youll end up on an "install Plugins" page.
3. click on the "upload" link (below the page title) and you'll get a file upload form.
4. browse for the Gravity Forms zip file you downloaded
5. select the file and click "ok" or "open" (depends on which browser you're using) and then click the "install now" button. WordPress will upload and unzip the file and then it will take you to a page to let you know the file was uploaded successfully.
6. Once you're to this screen, you'll need to click on the "Activate Plugin" link. Once you've done that, you'll be redirected back to the main plugins page and you'll see Gravity Forms in the list.
7. Now the form is active, but to be eligible for automatic one click updates, you'll need to go to the Gravity Forms settings page (click on the forms toolbar on the left, and then settings link) and enter your license key (from the email you received when you made your purchase) in the first field.
8. Once you've entered your key, click on the "Save Settings" button at the bottom of that page and you're done.
If you need more information about installing plugins, there's more in-depth information on the WordPress codex.