Go to the "Assets overview" in your Account on BTCMEX.
You will find Wallet Balance, Margin Balance, and Available Balance information here.
The Wallet Balance is your Deposit + Realized PNL.
The Margin Balance is your total equity held with the exchange, or Wallet Balance + Unrealized PNL.
The Available Balance is your margin available to open a new position, it consists of Margin Balance - Order Margin - Position Margin.
Information about your open position, Order Margin, and Position Margin is also available here.
If you have the BTCMEX Trading Bonus, it will be displayed in the "Assets overview" as well.