We usually have 2 accounts for each fixed asset category (i.e. motor vehicles) - the cost account and the accumulated depreciation account.
When a fixed asset is purchased, the cost is Debited to the appropriate cost account (Cr Cash or Payables Control).
At the period-end, a depreciation charge is made on most fixed assets. This account is Credited & a Dr is made to the Depreciation Charge account (this is an expense whereas the accumulated depreciation account is carried forward in the Balance Sheet - offset against the relevant cost account). The amount of depreciation charged depends on the type of asset. This adjustment is often best left to your accountant.