The Media Manager of Joomla! allows you to sort all the media files you want to add to your website and also to insert them in your contents.
To access the media manager, select Content → Media Manager. You will see the following page:
1 - Upload new media from your local environment. You can upload several media at once.
2 - As is the case for the categories, it is recommended that you build a tree view for your media files. If you put them all in the same folder, it may be hard to find your way around your media files when there'll be lots of them. Thanks to this button, you can create new folders and sub-folders.
3 - You can delete one or multiple media or folders at once. You just need to check the boxes of the media or of the folders you want to delete and then click the Delete button. You can't delete a folder containing media files, you first have to delete all the media files that are inside this folder.
4 - You can define many parameters such as the allowed extensions, the maximum size, the folders location path (by default, they are put into the directory /images) and the media manager permissions.
5 - Here is the tree view with your folders and media files.
6 - You can open the media manager in two different views: Thumbnail View or Detail View.
7 - You can navigate through your tree folders and files.
Media manager in contents
Each time you use an editor to edit a content (e.g. articles, categories, some modules like the custom content module or also contact forms), you will have access to the media manager thanks to the Image button, below the editing text area (1):
Image button when editing an article
When you click the Image button, the following window pops up:
Media manager when editing content
All you have to do is to select the media you want to insert (1), define the alignment (2) and then click the Insert button (3). If you scroll down towards the bottom of the window, you also have here the possibility to directly upload an image from your local machine to the server.