A user's guide to Penrose graphical notation?

Penrose graphical notation seems to be a convenient way to do calculations involving tensors/ multilinear functions. However the wiki page does not actually tell us how to use the notation.

The several references, especially ones with Penrose as author, must be good places to start. But it is now the summer holiday and I am away from my school library. So I am wondering whether someone here has a nice introduction to "the use" of Penrose graphical notation.

Thanks!

There are nice notes from a tutorial given at Siggraph in 2002 here : http://research.microsoft.com/apps/pubs/default.aspx?id=79791

There is succinct medium article covering it from the ground up. I am not aware of anything that goes into too much apart from what the previous answer points to

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