What's a TFSA?
The TFSA is a savings account into which anyone 18 years of age and older can contribute $5,000 a year tax free. The type of eligible investments available will be similar to RRSP's, but the gain you set aside for savings will be taxed differently.
The advantage of TFSA is that you can use the money you put into it as you wish, and tax-free. You will be free to take the money out including capital gains without having to pay taxes on money earned in the TFSA account. Plus, you'll have the option to put the money back into your account whenever you like. Any amount of your withdrawal will be added to your contribution limit for the following year.
Withdrawal won't make any effect on your Old Age Security Benefits.