GCFLearnFree's YouTube channel has videos on a wide range of subjects, including Microsoft Access. The videos start with the absolute basics, introducing the background concepts and simple single table databases (very useful for the IGCSE Computer Science course). They then move on to more complex topics such as designing different types of queries, creating forms, and formatting reports. Video are generally less than 5 minutes, which means they get straight down into the details and make it easy to skip to the right part. The video focus on Access 2013 but students should be able to adapt the techniques to other versions too.
A good overview of database theory, which is sufficient to cover the syllabus for most GCSE courses, and is a good introduction to the topic for A Level and IB courses. The differences between structured and unstructured data are covered, along with database basics (fields, records, tables). The second half of the video explains relationships in more detail, including 1-to-1 and 1-to-many relationships.
This site lets users try out queries and commands using SQL. The supplied test databases has a dozen tables and hundreds of records, and can easily be reset if a mistake is made. Although SQL is no longer part of the Edexcel Computer Science syllabus, this is still a great site to help students understand what queries are and how they work.