The best way to learn SQL is by using it. The four basic things you need to know are Select, Insert, Update, and Delete.
SELECT [columns to select] FROM [table] [where] [order]
INSERT INTO [table] ([names of fields to insert]) VALUES ([values to insert into respective fields])
UPDATE [table] SET [field name 1]=[value 1], [field name 1]=[value 1] [where]
DELETE FROM [table] [where]
[table]-> the table you want to modify
[field or column name]-> the column in the table you want to modify
[where]-> tell which rows of the table to modify. Usually looks like "WHERE ID=1" or "WHERE ID like '%1%'" or "WHERE ID IN (1,2,3,4,5)"
[order]-> the order by clause tells how the values should be ordered. "ORDER BY Create_Date" or "ORDER BY Create_Date DESC"
That should get you started. Then look at Joins, nesting, etc. Good luck!!