[alt-photo] Dilution calculation

[Jon Reid]

Dear list,
Would someone be kind enough to either explain how to work out
dilution calculations or how to use one of the online calculators?

Several online dilution calculators have units and symbols I don't understand.

I have 20% Na2 and I'd like to create some 2.5% and 5% solutions.

Further, what's a good method for accurately measuring small amounts
of solution? Do I need a pipette?

Jon