From outside, one might think that the notation is universal and unchanging, nothing could be further from the truth: each field has its own take, its own conventions. One even finds groups within a field who "go their own way", and there are national differences too. Sorry.

Realistically, find a paper that interests you, hopefully they will list some expository text in the references (or a paper that they cite does). Get it and read it. There's not really any alternative if you want to understand the notation, it represents complex ideas compactly, so you need at least a basic grounding in those ideas.