The birding resources I use most often come from the Cornell Lab of Ornithology These fine folks are worth supporting, through memberships, subscriptions, and/or donations.
Merlin This phone app is a great tool for bird identification in the field. I usually don’t spend much time on identification while I’m walking around — my routine is to use my photos and take my time once I’m home. But in support of my photography efforts, I’ve found it useful to know what I’m looking for, and try to anticipate shots based on behavior. The Sound ID tool is amazing for this. One example: at a very bird-busy spot one fall trip, the app generated a long list of birds from their songs that included Cedar Waxwing, a favorite and very photogenic bird whose high whistle sometimes gets lost in a crowd (to my ears). Knowing that they love their red berries, I scanned for berries in the bushes, and when I spotted some, there were the waxwings. Click. The only negative is the risk of spending more time looking at my phone instead of looking for birds.
eBird This site is useful for checking sightings from birders at specific locations, and a great place to maintain trip reports if that’s something you want to do. I’ve been meaning to submit information here to help others, but I haven’t yet built that into my routine.
All About Birds A good overview for each bird, and tools for identification, including very useful comparisons with similar species with text and photos.
Birds of the World (subscription) Encyclopedic information for each species of bird. I’ve subscribed on and off; at about $50/yr (sometimes discounted), I feel like I don’t use it enough to justify the cost. But it’s a great online resource for deep dives.
I occasionally use Google Search for images, using either a text description of the bird I’ve seen, or pasting in a photo if I have one. If Merlin gives me too many similar ID choices, I sometimes find it helpful to scroll through a bunch of images until something looks like a match, and then following that link.
Field guides: I like the Sibley guides, but as with anything, if you want a range of opinions, check the Internet. I use the flex-bound “Sibley’s Guide To Birds”, which seems a good balance of size and detail. Other folks like the regional versions and different sizes.
Sibley also has a lovely collection of images and information called “What It’s Like to Be A Bird.” It is organized by themes rather than species, and it is big and heavy, so it’s not appropriate for the field, but it’s great for flipping pages and learning more about birds during gaps between outings.
I’ve also enjoyed books by Jennifer Ackerman; I’ve read “The Genius of Birds” and “The Bird Way.” In both she presents a good balance of research and anecdote, giving a good overall sense of what birds can be like.