Your work experience is the list of all the jobs you've ever had. If you are an accomplished dog walker and a pretty good babysitter, those are both part of your work experience.
Work experience is just what it sounds like: it's all the experience a person has had in their work life. This can include both job titles and actual skills learned. When someone applies for a job, they're almost always asked about their previous work experience. If you want to get hired at a daycare center, it makes sense to focus on relevant work experience like babysitting — they'll be less interested in your lemonade stand!