Putting files in a post the easy way, by dragging and dropping into the area that is indicated here. It will change opacity and have dotted lines to confirm that it is activated.
Couldn't be easier !
And a free Tip : Once a file has been uploaded, you have 2 options for the file (indicated by the two red circles)
1- the circle with a cross, when clicked, will insert the file at the cursor position, in the editor's window.
2- the garbage bin will delete the file when clicked.