WooHoo is an action that Partnered, Engaged or Married Sims can do, corresponding to making out or having sex. The action takes five minutes.
In the 2015 Royal update, they can now WooHoo in a bed if one is available.To do the action, you tap on the Sim that is Partner, Engaged or Married and click on 'WooHoo' option on the top right side. They will then go to a bed and hearts will float up. If one isn't available for them, they will switch into their swimming clothes (or underwear if they do not have any) and kiss each other under a blur while hearts come off of them. They can WooHoo in a tent or just any location.
Sims can only WooHoo once players complete the 'Love Is In The Air' quest. If players use the 'Be Romantic' option and WooHoo before the goal tells them to, then it won't register that you've done it and you might have to redo it.
It is also possible to have multiple couples of Sims WooHooing at the same home lot, or even in the same room.