After the Exploration phase, you've collected a lot of information. The goal now is to cluster it and define where you want to go.
To do so, you should gather the team, start writing on post-its all the "interesting" discoveries you did and sort them to create themes.
Let's say you are working on a service design project: a tourism office (I'm just inventing here). After some research and interviews you've discovered young adults don't like going through all these brochures and fliers you can find there. They don't really know if it's worth it depending on their budget, likes and schedule. Today with internet and blogs, they are used to get feedback, advices and that is why they don't go to tourism offices anymore. And somehow you've experienced the same kind of talk with older people who want "everything to be ready", to fit their tastes. The theme here could be "Personalization".
From this theme you can then rephrase it as 1-3 short sentences: the insight, a short, concise statement that opens to new possibilities. You should do that for every theme, discuss and end up with a maximum of 5 insight statements that will help you take a direction for the next phase of your process.
In our example, the insight for "personalization" could be: "I like checking what I can visit or do on holidays because then I don't have regrets afterwards. But in the tourism office I would waste hours finding exactly what fits with my tastes and wallet without being sure if it's worth it. I wish I could find more personalized info with feedback."
(Like Trip Advisor does actually, but this is just a random example I took to explain).
Once you have your list of insights, you have a strong basis to continue the process, especially to do brainstorming, co-creative sessions and to create "How might we?" questions.