Write one calculation per line, and the result appears next to it. That is all there is to it. Pick the task below that looks like yours, copy the lines into a new sheet and change the numbers.
Everything on this page is free unless the heading says Pro. The full reference explains every rule and function — you do not need it to get started.
Add VAT, or take it out
+ 19% adds 19 % of the amount. To go back, divide by 1.19: writing gross - 19% would take 19 % of the gross price, which is not the VAT.
Discounts and markups
Convert units
Write the unit right after the number. in converts; without it the result keeps the unit you used.
Split a bill
Add up a list
A line with just total adds up the numbers above it.
What a trip costs
Hours worked
Clock times can be subtracted; the result is a duration.
Days between two dates
Dates are shown in your device's format; Settings → Date format fixes one.
Savings with interest
Monthly loan payment Pro
The payment comes out negative because it is money you pay.
Average of a few numbers Pro
Without Pro: (1.7 + 2.3 + 2.0 + 1.3) / 4.
Draw a chart Pro
Turn a sheet into a form Pro
Give your numbers names (capital = 1000 €), then open Form → Edit form…. There you add input and output fields yourself, or let the editor suggest them from your sheet: Apply all takes every suggestion, or you tick single ones. Form → Form view then switches between the sheet and the form — handy for a calculator you hand to someone else. See Form view.