Vinyasa yoga is a dynamic movement style within yoga that is a bit more "flowing" than other forms of movement we might see in yoga. It typically links breath to movement to create a flow, or sequence of linked postures.
Typically, there will be a warm up sequence, which will build up to some slightly more challenging positions. This isnt always the case though.
The class could be fast, or slow and quite chilled out. Theres a lot of variation within this style, so its good to check with the teacher you're going to and ask how they teach it and what its like.
For myself however, I really love to teach vinyasa. I like to teach it a slightly slower pace, and I absolutely love to break things down. For instance, breaking a posture down into the movements the body needs to do to get theree, and how to get there.
I really love to focus on the foundations of the postures so we can feel strong, capable and prepared for our practice, while having a bit of fun along the way.