The S1 license contains 9 cars and 4 tracks in total. In other words, all demo content + 6 additional cars and 3 additional tracks. In addition to more cars and tracks, buying a license enables up to 40 grid slots and 79 connections online, selecting reversed track configurations, building custom autocross layouts, uploading custom car skins without having to buy extra slots, and using all lfs.net website features.
The base price for S1 license is £12, however it can cost £9 or £6 depending on the user's country. You can see the prices for each country on the voucher selection page.