Welcome to DA and welcome back to YGO, you've joined the right place to help you back into the game.
Firstly here is Pendulum mechanic explanation, but pendulum is due to change with tmecanhic. The only is that Pendulum will no longer have there own zone and will be placed in the S/T zone instead.
https://youtu.be/Gs08XuC62LU
Here is the Link mechanic explained
https://www.google.co.uk/url?sa=t&source=web&rct=j&url=https://m.youtube.com/watch%3Fv%3DWSyZfhvYhz4&ved=0ahUKEwi684uH__TTAhXHJsAKHRoqBLoQwqsBCDUwAw&usg=AFQjCNFnK1j619f8o0lyqysQzkUR6XjH6Q&sig2=mTydRakcxfn4AG0LKQRpUw