Sharing With All Your Facebook Friends
If you want to share a thought or photo with everyone you're Friends with on Facebook, you'll want to write it in the Status Update area. The Status Update area is the box that says "What's on your mind?" (pictured below)
If you're still not sure where this is, click the small Facebook logo in the top-left corner (pictured above) Once you do this, the page should load up and show you the "What's on your mind?" box at the top of the page. Now you can type whatever you'd like to share or click Photo/Video to add one of those! Click Post when you're ready.
Note: The Friends box directly to the left of the Post option means you're sharing this text, photo, or video with all your Facebook Friends. You can click it to see more options, but I'd recommend keeping it as Friends for now.
Sharing Directly with One Person
If you want to share a message or photo for one person specifically, such as a cute "I love you" message or perhaps a photo, you'll want to go to that person's Profile page. To do this, start typing their name in the "Find friends" box at the top of the Facebook page (right next to the small Facebook logo in the top-left corner). Click the name when it pops up.
Once you click the name from there, you'll get to the Profile you want. Now find the box that says "Write something to" and the person's name in it (pictured below). Start typing away!
Note: Sharing a message or photo this way is not private between you and the person you're sharing with. Others can see potentially see this. If you'd like to send a private message between the two of you, you'll want to use Facebook Messenger (guide coming soon!).