Your broadband speed isn't up to the job, which is why you're suffering 'buffering' problems.
Other than getting a better broadband connection, there's nothing that you can do about it except for waiting for the whole of the video to load before attempting to watch it. (i.e. brew a cuppa while it's stopping and starting and then click on 'Replay' to watch it uninterrupted).
Alternatively try watching it at a time when internet traffic is light, such as early tomorrow morning. (That's because you effectively share your connection to the internet with several other users. The number of other users is determined by your ISP's 'contention ratio'. If you're using a budget provider the contention ratio might be 50 to 1 - meaning that you share with up to 49 other users - or even as bad as 200 to 1. Connecting at 'off peak' times gets you a greater share of the available capacity).
Chris