To upload media files into your WordPress Media library, login to your WordPress dashboard and proceed as follows:

• From the left side pane, select Media.
• Click on Add New.
• Now, Upload New Media window opens up.
• You can directly drop files here by dragging them from your system.OR
• Alternatively, click on select files.
• Now, browse your system and select a file.
• The file will get added into your WordPress library.

(You can also upload the media while adding a page or blogpost by selecting Add Media >> Upload Files and then followed by the above mentioned process)