So basically you want to know how to join one set of data to another in Qlik Sense?
Qlik performs association on columns named the same. So if dataset A has a column in it that matches the name of a column in Dataset B Qlik Associative data model joins the two sets on this column.
If you had 2 sets with a country identifier the Dataset A uses country codes (GB,DE) and Dataset B uses country names (United Kingdom, Germany) the data model will match the columns but you not get any joins as there are no matches on the data.
If you had 2 sets with a country identifier the Dataset A uses country codes (GB,DE) and Dataset B uses country codes (GB,DE) the data model will match the columns and you will get relationships between the datasets so joining the data in A with the one in B.
1. Make sure your fields you want to join on are named the same and the fields you want to remain unique are not.
2. Make sure the data in your join fields are in the same format.
Use your own data as that's the best way to learn. Wikipedia is a good source for play lists. you can also practise cleaning the data up.
Hope this helps you get started and good luck in your new job.