Hi @lester.fajardo, There are many cron-expression creator online which are easily understandable.
For eg : Free Online Cron Expression Generator and Describer - FreeFormatter.com
You can provide Sec/Min/Hrs/Day/Month/Year according to your requirement and see what kind of expression you get. There are many samples as well. If you have an expression already and want to know how it is described that also can be checked out.
I just gave the conditions you have mentioned and the tool gave me the expression. Please check it out and try yourself if possible. You may need to do 1-2 test runs to make sure its working as expected.
The cron I have used here is : 0 */15 7-19 ? * MON,TUE,WED,THU,FRI,SAT *