The Categories tab holds the useful life for each class of asset — computers, furniture, machinery, vehicles, buildings — which you can edit to your own policy; the straight-line rate is derived automatically. On the Assets tab you pick a category from the dropdown and enter the cost and purchase date, and the schedule fills in: annual depreciation (cost ÷ life), age since purchase, accumulated depreciation (capped at cost) and net book value.
The Dashboard totals your asset cost, accumulated depreciation and total net book value as at any date you choose, so you can drop the figures straight into a balance sheet. The formulas are locked and only the yellow cells accept typing, so the register can't be broken by accident.
It uses straight-line depreciation, the clearest method for accounts. For tax, confirm the current KRA wear-and-tear (investment) allowance rates, which differ by asset class and use a reducing-balance basis — a note on the Categories tab reminds you.