How do I open/close a Margin position?

When you want to trade on margin, funds need to be in your margin wallet. (How do I transfer funds between my wallets?)

To open a position:
1. Go to the trading page (https://www.bitfinex.com/trading),
2. Select the desired pair to open your position and choose Margin in the order form (not Exchange).
3. Setup a Margin order by specifying the amount, order type, price, etc.
4. When your margin order executes and opens or increases your position, Bitfinex will automatically acquire funding for you at the best rate currently available. Alternatively, you can manually reserve funding via the Funding tab at any time and use it when you decide to open/increase a margin position.
Optional: Selecting “Advanced Funding Options” (3 vertical white dots) in the Order Form box provides quick access to funding parameters.

To close a position:
When you decide to close an open position, you can either use the "close" button (a Market margin sell or buy order will close a long or short position, respectively) or place an order in the opposite of your open position with the same amount as your open position. When the order is completely filled, the position is closed, borrowed funds are repaid, and profit/loss will be credited to your margin wallet balance.

Instead of closing a position and you would like to claim it, read more details here: What does it mean to "claim" my position?