For the sake of the keeping things simple (Which is my model) the hotter it is outside, typically the higher the density altitude. The higher the density altitude the more of a DECREASE in aircraft performance you will find.
A perfect example of this is a stock 2011 ford mustang gt with drag slicks could run a 12.5 second quarter mile in Denver Colorado on a hot summer day. That same exact car, could run a 11.2 second quarter mile on a cool spring day at sea level.
Density altitude is HUGE in aviation. In effects how much runway you need, your climb performance, your landing roll, and even how much fuel you burn. Density altitude for lack of a better description is the altitude the aircraft feels like it's at. An example is the field elevation at my home airport of EYE. It is around 800 feet. However today the temperature is 32 degrees Celsius, with a barometric temperature of 29.88inches which gives us a density altitude of about 3,000feet.
Here's a simple chart that's used to calculate it.
