It is the right to depreciate a capital asset, namely up to 4% a year of any improvements (i.e. house, buildings, new balconies, new roof..).
To do that estimate the land value and deduct it from your purchase price. You can then use up to 4% of that annually to reduce your taxable income, frequently to zero.
Do not use CCA in years where there is a loss already, say in a start-up year or a weak year with many vacancies.
The CCA has to be repaid later, so it is really a tax deferral strategy. So, as an example, if over 5 years you deducted $20,000 in CCA you will have to add this $20,000 to taxable income in the year of disposition.