Hi Chris,
Plenty of free tutorials on SQL out there, including interactive ones (search for "SQL interactive tutorial" in a search engine, plenty of results).
I suggest you download a SQL browser so you can explore(=view) the content of the SQL file generated by E+ AND try your queries. I personally use https://sqlitebrowser.org/ since it works nicely and it is cross-platform (I use all three major ones, windows, mac, unix, so I appreciate consistency)
For your thing, it's just about 1) Filtering the rows you do want to keep (be as specific as possible to avoid surprises), and 2) doing a groupby
Here's the basic query:
SELECT Month, Day, Hour,
    SUM(Value) as 'Total OA Mass Flow Rate' From ReportVariableWithTime
WHERE EnvironmentPeriodIndex = 3
 AND Name = 'Air System Outdoor Air Mass Flow Rate'
 AND ReportingFrequency = 'Hourly'
 AND Units='kg/s'
GROUP BY Month, Day, Hour
ORDER BY Month, Day, Hour
    SUM(Value) as 'Total OA Mass Flow Rate' From ReportVariableWithTime
WHERE EnvironmentPeriodIndex = 3
 AND Name = 'Air System Outdoor Air Mass Flow Rate'
 AND ReportingFrequency = 'Hourly'
 AND Units='kg/s'
GROUP BY Month, Day, Hour
ORDER BY Month, Day, Hour
Here I specify EnvironmentPeriodIndex = 3 because I have run the simulation for two design days, and I do not want to count the design day flows (without it on 7/21 it would sum my annual sim + summer design day)
Name is self explanatory
I Specify reportingFrequency='Hourly' to ensure that I also do not any potential same variables I may have requested at a different timestep (eg: 'Timestep')
I specify Units='kg/s', but you could not do it since there isn't a variable with the same name and different units
Result
Now, if you want to get fancier, you can generate a timestamp on the fly...
SELECT strftime('%Y-%m-%d %H:%M', '2005-'|| substr('0'||Month, -2) ||
     '-' || substr('0'||Day, -2) ||' '|| substr('0'||Hour, -2) ||
     ':'|| substr('0'||Minute, -2))
     AS 'Timestamp',
    SUM(Value) as 'Total OA Mass Flow Rate' From ReportVariableWithTime
WHERE EnvironmentPeriodIndex = 3
 AND Name = 'Air System Outdoor Air Mass Flow Rate'
 AND ReportingFrequency = 'Hourly'
 AND Units='kg/s'
GROUP BY Timestamp
ORDER BY Timestamp
     '-' || substr('0'||Day, -2) ||' '|| substr('0'||Hour, -2) ||
     ':'|| substr('0'||Minute, -2))
     AS 'Timestamp',
    SUM(Value) as 'Total OA Mass Flow Rate' From ReportVariableWithTime
WHERE EnvironmentPeriodIndex = 3
 AND Name = 'Air System Outdoor Air Mass Flow Rate'
 AND ReportingFrequency = 'Hourly'
 AND Units='kg/s'
GROUP BY Timestamp
ORDER BY Timestamp
I hope this helps!
Best,
Julien