First, sign up for an account!
Next, create a group. Groups are an easy way to split expenses with a particular group of people on an ongoing basis. For example, you might create a group for your apartment, or a group for a ski trip. As part of creating a group, you'll be asked to provide contact information for the other members of the group. This allows all of those people to view the group on Splitwise, and to add expenses of their own. Splitwise also lets you add "non-group expenses" for items that don't deserve an entire group, like going to dinner with a few random friends.
Once you've created your group, you and your friends can all start adding expenses! Go to your group, then hit the "Add bill" button. You'll be asked for various details about your expense, like the total cost, who paid, and how much each person should owe. You can include a picture or additional notes, or even change the date (for example, if you're adding an expense from last week). As soon as you hit "Save", Splitwise will update everyone's balances to keep track of how much each person owes.
Later, after you've added a bunch of expenses, you'll probably want to settle up with your friends. Just hit the "Settle up" button to pay back your friend. You can record a cash payment (e.g. you just handed your friend some cash, and now you want to update Splitwise to reflect that), or if you're in a supported country, you can send your friend a PayPal or Venmo payment directly through the Splitwise app. Electronic money transfers will be delivered to the recipient's email address.
Those are the basics, and should be enough to get you started. If you have more questions, check out the rest of our helpdesk articles!