Well within this forum, probably main approach would be to search using search terms, peruse the proper threads and then understand the broad categorization of military equipment into its various generations/eras. Then you can ask specific questions in those threads for more details in say A vs B of same generation platforms.
Other than that google is your friend.
Or you can read the wikis of worlds largest armed forces and note their equipment and force structures....what is legacy technology, what is current technology and what is being developed for the future etc. Maybe start with this and then branch outwards into this forum pertaining to your interests in the suitable threads.