To edit a page, master, or project level property in a shared project, the page (or master, etc.) must first be checked out. To check out a page, right click on the page in the Sitemap pane and select Check Out. Checking out a page will also update the page if changes were found in the shared project. Additionally, some project properties may be updated. Once the page is checked out, it can be edited normally. Checking out the page reserves it for you to make changes and (mostly) prevents others from editing that page.
If you try to check out a page that is already checked out, you will be notified. You can however choose to edit the page anyway by doing an Unsafe Check Out. This is not recommended because it can result in a Conflict. A conflict occurs when multiple people make changes to the page at the same time. Only one person’s changes can be saved in the shared project. The other changes may be lost or overwritten and will need to be reapplied manually.
Unsafe check outs are allowed in case the page (for whatever reason) cannot be checked in from the computer where it is checked out, or if you are unable to connect to the shared directory.
To check out multiple pages, select the pages in the Sitemap holding the Ctrl key for multiple selection and right click to select Check Out.
To check out the entire project, go to Share->Check Out Everything. This will check out all the pages, masters, and project level properties.