A hedge fund will generally have three kinds of positions: Cash, Long Positions and Short Positions.
You find the value of long positions (VLP) by adding up the dollar values of all long positions. You find the value of short positions (VLS, which will be a negative number) by adding up the dollar values of all short positions.
Then the Total Equity is defined as TE = Cash + VLP - |VLS|
The dollar net exposure is DNE = VLP - |VLS|
The dollar gross exposure DGE = VLP + |VLS|
The percent net exposure is %NE = DNE/TE
The percent gross exposure is %GE = DGE/TE
The cash exposure is %CASH = Cash/TE
(A fund with zero gross exposure will be 100% in cash).