Something that's afoot is already happening, underway, or being prepared. You might reassure your fellow French club members that plans are afoot for a fund raiser to support your upcoming trip to Québec.
People frequently say that plans are afoot when they've started preparing for a party, an election campaign, a job hunt, or anything else that requires some planning. Plans might be afoot for your dad's surprise party, for example, or your sister's wedding. Another, less common way to use afoot is to mean "on foot," or "walking." You could tell your teacher that you're late to school because you missed the bus and had to travel afoot.