For the real table names, you can just change the table1/table2 and leave t1/t2 as is, or you can switch the t1/t2 to use the full table names, or you can come up with your own alias
(I generally use the first one/two characters of each word for aliases - less typing but still understandable within the context).
I tried to find a good explanation of what the "LEFT JOIN" and "SUM/GROUP BY" bits are doing, but couldn't find anything that looked useful.
A left join is basically lining up all the rows in a pair of tables, but unless a regular "inner" join, a left join says "if I've got a row on the left table, but not on the right table, still include it". (any rows in the right table but not on the left are excluded from a left join). In this case it means anything without any spares price is still listed - with a regular join it would not be.
The sum function is an aggregate function, meaning it applies to multiple rows - (it adds the numeric values of a bunch of rows) - which you identify by grouping together rows using the group by command at the end.
I wish to thank Peter for his help over the last couple of week on this access DB, he is a gentleman and will receive all the biscuits and tea he asks for from now on!