1. Set up the two accounts if they don't exist yet. Under Chart of Accounts, create a Depreciation Expense account (type Expense) and an Accumulated Depreciation account (type Fixed Assets, detail type Accumulated Depreciation). Accumulated Depreciation is usually set up as a sub-account under the fixed asset it tracks, so it nets against that asset on the Balance Sheet.
2. Work out the depreciation amount for the period. QuickBooks doesn't do this math for you in Online, and standard QuickBooks Desktop doesn't either (Desktop's Fixed Asset Manager, available on Premier and Enterprise, can calculate and post it, but that's a separate add-on module, not the base product). Straight-line, declining balance, whatever method your accountant uses, the result is a dollar figure you bring to QuickBooks already calculated.
3. Head to the journal entry form. Click + New, then look for Journal entry under the Other column.
4. Debit Depreciation Expense. Enter the amount for the period against the Depreciation Expense account.
5. Credit Accumulated Depreciation for the same amount. This is the balancing line. Add a memo naming the asset (or asset group) and the period, so whoever reviews this later doesn't have to guess what it covers.
6. Save. Repeat on whatever schedule matches your depreciation method, monthly or annually, for each asset or asset group you're tracking this way.