When modelling parts in CAD software 90% of the time users would start by creating a sketch. A sketch is a group of lines or curves laid out to create a shape in 2D. This if you like is the foundation, these shapes can be dimensioned to specific sizes using measurements. This is what is known as parametric modelling. Fusion 360 has two different workflows, Parametric modelling and Direct modelling.
The easiest way to define these are, Parametric modelling records the history in form of a timeline at the bottom of the screen. Each command displays a small picture on the timeline to identify it. Users can re-visit these commands at a later date and make changes to the model and allow the software to regenerate the model based on the changes made.