I got most of my information from https://www.interaction-design.org/literature/article/what-is-design-thinking-and-why-is-it-so-popular (01/09/20) and added some of my own ideas.
Design thinking is a type of thinking that is useful to find solutions to "unknown" problems. Design thinking includes re-framing the problem, brainstorming to come up with ideas for solutions, and a lot of experiments in order to find the best solution (prototypes, running tests, trying out all ideas, etc.).
There are multiple different steps for design thinking, including:
These strategies can be in any order and you can do some multiple times, it all depends on the specific project.
There are multiple phases/steps of design thinking, as well. These phases don't follow any specific order and can be repeated as many times as needed. There's many different versions of these phases, that all have the same principles. I'll focus on a 5-phase plan created by the Hassoplattner Institute of Design at Stanford (d.school):