Please go to the section "Video", in the upper right corner there will be a button "Add video". So you can upload the video from your computer or add it from another video hosting, for example, from https://youtube.com or https://vimeo.com.
To add a video from another video hosting, click on "External video" and specify the link to the video in the "Link to video" field.
To upload a video from your computer, click on "Add Video" — "Select file".
After uploading the video, enter its name and description, and then click on "Save".
Open the section "My Videos". To delete a video, hover over it with the mouse and click the ellipsis "..." in its upper right corner, select "Delete" in the drop-down list. Unfortunately, there is no way to delete all the videos at once.
Open the section "My Videos". To edit a video, hover over it with the mouse and click the ellipsis "..." in its upper right corner, select "Edit" in the drop-down list.
Open the video, next to the "People in this video" block, click "Mark people" and specify the username that you have as friends — those who are not, you will not be able to mark.