Read the standard. There truly is no way around it if you need to perform actual "real" work with DICOM. You need to become familiar with the vocabulary. Also get a copy of [0]. Write a small C program that outputs whether a file is in DICOM format or not (don't do extensive validation, but learn enough to know what to look for). Will you be doing networking? If so, read the standard. Use Wireshark. Look up the DUL state machine and read some library's net code (e.g. pynetdicom).

[0]: https://www.springer.com/gp/book/9783642108495