How to ORDER BY a SUM() in MySQL?

The problem I see here is that "sum" is an aggregate function.

first, you need to fix the query itself.

Select sum(c_counts + f_counts) total, [column to group sums by]
from table
group by [column to group sums by]

then, you can sort it:

Select *
from (query above) a
order by total

EDIT: But see post by Virat. Perhaps what you want is not the sum of your total fields over a group, but just the sum of those fields for each record. In that case, Virat has the right solution.