You can control Read/Write access to Site assets through Access rights. Access rights, or permissions, control which Users or Groups can view or edit assets. While viewing an asset (such as a Folder):
Click More > Access.
Select the Access level for all users. (Selecting None here will hide the asset from all users except Administrators and specific Users/Groups granted access in the next step.)
Grant Read/Write access to specific Users/Groups using the chooser.
Folder and Container assets have an additional feature called Access for Contents which allows update the access rights for the contents of that Folder/Container. While viewing a Folder, click More > Access for Contents.
Updating the access rights on the contents of a Folder/Container can be performed using two different strategies:
Merge Access Rights: Merging will add new assignments to all contained assets where the User or Group specified is not already assigned. If the User or Group is already assigned to an asset, then the Access level (Read or Write) will be updated with the new value specified. All other existing User and Group assignments will not be changed.
Overwrite Access Rights: Overwriting will remove all existing User and Group assignments on all assets within a Folder and apply only those specified. Be cautious with this option. In most cases, you will want to Merge Access Rights as opposed to overwriting them.