The skills section is about developing yourself as a person. You can improve at something that you already do, such as photography, or try something that you have always wanted to have a go at, such as computer programming.
It can be something inside or outside of school; you just need someone to sign off and confirm your attendance at the end of your chosen time period. If you join a club in school, such as media club, you can ask the member of staff that runs the club. Outside of school, you can ask the club organiser/your coach etc. While it is unlikely that they will say no, please check with the club organiser/your coach etc before adding their name to your Skills section.
This is the one of the four sections that people often find the most tricky. There are plenty of activities that could be considered a skill, but for the purposes of DofE, would be more appropriate to use in the physical or volunteering section. If in doubt, please ask a member of staff at the Friday training sessions.
Some examples of the activities that past DofE participants have used for their Skills section include: playing a musical instrument, joining chess club, working towards a coaching qualification, improving their cookery skills and learning how to knit. If you are still stuck for ideas, this document may give you some inspiration. If you are still struggling, please speak to a member of staff at one of the Friday training sessions.