The local currency is the Ugandan shilling (USh), though most tour operators and upscale hotels quote in US dollars. ATMs are abundant and US dollars are widely accepted.
Tipping isn't expected in Uganda but, as wages are very low by Western standards, it will always be appreciated. The size of a given tip is up to the individual.
Restaurants USh1000 to USh1500 is enough in ordinary restaurants.
Rangers USh5000 to USh10,000 is reasonable for ranger-guides in national parks.