Click the upload now button, at the top of the screen. Then there will be a box in the middle of the screen, with a green bar saying select photos and videos, when you click it a window will popup and in it you will select the location and files that you wish to upload. You can select multiple files by holding down the Ctrl button located on your keyboard. When you have the files selected, click open and the files will be uploaded. You will now be sitting at a screen that shows the files you uploaded, you can add a title and description to them and then choose the save and continue button, located to the right side of the screen. You can create folders and organize your pictures also.
To post them, go to the album with the picture you want and hover over it, a bunch of links will be displayed below it, copy the img link and paste it in your post.