Blocked Plug-ins on MacBook Pro?

[Amzo]

so i just got a macbook pro and it's not new, it has been used. so when i try to go on any video websites, it does not work. for example, on youtube, i click on a video and it just comes up saying blocked plug-ins and does not play. It does this for every video. I have searched on the internet multiple times to try and find the solution but i have had no luck. i have tried going on to system preferences, then flash player but flash player is not there. Please try and help. If you have any questions just ask and i will answer them in additional comments or i will comment on your answer. thank you

Please try and answer, this is the second time I have asked this question
So in the small window it says Mac OS X version 10.6.8 Processor: 2.3 GHz Intel Core i5 Memory: 4 GB 1333 MHz DDR3 It also has a button for software update and a button for more info Also my maths is a website for schools to do homework Any help would be appreciated thanks