That's a great idea canva is very basic and easy tool for beginner in graphic designing and you can do lot of designing work through it. The paid version of canva is also a very good option for earning. If you want to be better in canva then you have to keep practicing on daily basis. You asked about giving free service for experience then I suggest you to BHW freebies giveaway section and also other social media platforms you use in daily life. Designing banners, posters, thumbnails and posts free for audience can also give you a loyal customers in future. You can also give your services on facebook, tiktok and instagram also.