On the Students tab you list each learner, the subject you teach them and the rate per lesson in KES. On the Lesson Log you add one row per session, the date, the student from a dropdown, how many lessons and whether they paid, and the amount billed is worked out from that student's rate for you. Each student's total billed, paid and balance rolls up on its own, turning red the moment a balance is owed.
The Monthly Summary totals your income billed, income paid and what is still outstanding for every month, plus a running grand total, so a term of scattered lessons becomes a clear set of numbers. Yellow cells are the only ones you type in; everything else is a locked formula. It opens in Excel, WPS or Google Sheets, so you can update it on your phone straight after a lesson.