Welcome to steemit! To upload your photo (assuming you are talking about profile picture) go to imgsafe.org. Upload the profile picture you want by using drag and drop and then once it is uploaded click on the image. Copy the link below the image.
Go back onto steemit.com and click your profile then click settings. Where it says profile picture url paste the image link you copied from imgsafe. Click Update near the bottom of the page and type in your master password (whatever it is called). Refresh the page and your profile picture should have changed.
It is the same for uploading a profile banner except obviously you paste the link into cover image url instead.
To upload a picture onto a post just click the button in the toolbar which says image when you hover over it (picture of a mountain with a mini sun). Then copy the image link from imgsafe and paste it in the box which drops down when you click the image button.