You just have to take a picture with snapchat's camera. Add effect, text, or draw on It and choose how Many time the picture Will be available for viewing (from 1 to 10s). Then, choose Who will receive your snap or add It in your story.
For adding friends, go on your list of friends and click on the button with 👱 and a +,shearch a user name. When you find who you wanted, click on the + next to the username. You can also syncronize your phonebook with Snapchat.
receive a snap
When you receive a snap, a little red square appear. Click on It and keep your Finger on the screen to see the picture (or video). You can "screenshoot" you friend too.
When you add a picture (or a video) on your story, your friends can see it during 24 hours. To add a snap on your story, take a picture and when you have to choose which friends will receive it, you just have to click on "my story".