You may typically sell in a particular currency, like Euros, but for an individual proposal it may need to be in a different currency, like USD.
It's easy to change your currency on a proposal. To do so, go to the right hand panel and select your currency from the drop down.
Then find your new currency in the drop down search.
On your sales pipeline, if you have proposals using different currencies, it will output the total for each currency below each status:
Keep in mind a few things:
You can't have one proposal with multiple currencies. If you update any pricing table's currency in a proposal, it will update all pricing tables in that same proposal.
You can't change the currency of a pricing table when editing a section in the content library — you need to be in a proposal.
You can only select currency in the proposal editor mode. Templates don't hold currencies.
If you change your default currency in your account settings it WON'T update the currency of proposals already created. You will still need to go into them individually if you want to change their currency.
Also see Default Currency