There are a lot of talks going around when it comes to adjustment of fixed assets and depreciation expense in accounting terms. Depreciation is almost similar to that of any other expenses in the fact that all expenses are deducted from sales revenue to determine profit. Keeping this apart, however, depreciation is very different from most other expenses. (Amortization expense, which we get to later, is a kissing cousin of depreciation.) When a business buys or builds a long-term operating asset, the cost of the asset is recorded in a specific fixed asset account. Fixed is an overstatement; although the assets may last a long time, eventually they're retired from service.
The main point is that the cost of a long-term operating or fixed asset is spread out, or allocated, over its expected useful life to the business. Each year of use bears some portion of the cost of the fixed asset. The depreciation expense recorded in the period doesn't require any cash outlay during the period. (The cash outlay occurred when the fixed asset was acquired, or perhaps later when a loan was secured for part of the total cost.