Sometimes, this is a once-only requirement – for example when you have already set up a user account. In other cases, however, you are required to click an ‘Accept’ or ‘Proceed’ option every time you perform the task, for example when downloading software updates.
The act of accepting Terms & Conditions does not, of course, mean that you have read them beforehand. Most people do not do so as either the Terms & Conditions are very long, or people simply assume them to be accurate and legitimate.
It is important to remember that accepting Terms & Conditions constitutes a legally-binding contract, so it is in your interest to make sure that you have read them before accepting. In doing so you will also be satisfied that the agreement you are entering into suits you as well as the supplier or website owner.