Don't be discouraged if figuring out which species you've observed is more difficult than you expect! Many organisms you may recognize, and know the common name for, refer to several specific species. Is it a Common Dandelion or a Red Dandelion? An Eastern Chipmunk or a Least Chipmunk? While it is tempting to just pick the species most common to your geographic area, this leads to missing changes in a species' range, or the start of a new invasive species. What if no one thought it could be an Asian Longhorn Beetle because they're only found in Asia?
It's frustrating but the best way to get better at identifying species is to practice, and take the time to be confident of your IDs so you don't build bad habits. Below I list some resources from iNaturalist on becoming a better IDer, as well as some online field guides available to the UMass Amherst community (you will need a NetID) and species keys freely available online.
Remember that iNaturalist is a community! If evergreen identification isn't your strong suit, there may be someone in the community just itching to try out their New England arborist certification. If you have no idea what species of tick you found on your dog, take the best photos you can and don't worry about IDing more specifically than "tick" when you post it - I know there are tick ecologists on iNaturalist personally.
I recommend you only ID to the level you are confident. If you're sure of the Genus but don't know which of the dozen species it is, leave it at Genus! If you're only sure of Order, Family, or even Kingdom, leave it at that. There are filters on iNaturalist that will help people who are experts find observations which "Need ID" by any of those categories.
iNaturalist has robust help documentation, including video tutorials, details about how the platform works and community standards, and advice on improving your observations and species ID skills. Here are some links to Species ID resources to get you started:
Use species keys to narrow down your choices to a specific species. You already do some of this when you count the legs on the small scurrying insect and determine it's an arachnid because of the 8 legs. It's a game of Guess Who, eliminating the possibilities based on observable characteristics, until you're left with the right one. Do the needles of this evergreen come in groups of 2, 3, or 5? It takes patience and persistence, and it's the way that professionals train to identify the correct species.
There are a wide variety of field guides, from the general ones that cover the most common species in a certain geographic region to much more specialized ones that focus on a particular phylum, class, order, or family, or a much more specific area, or both. They help you identify the species of your observation in a different way than a species key [above] does, relying much more heavily on a general visual match, though many field guides also include partial species keys for trickier characteristics. For the City Nature Challenge, I've highlighted guides the UMass Libraries own which cover organisms within the Pioneer Valley.
The University of Massachusetts holds many field guides in both physical and eBook formats. Members of the campus community can access the eBooks with their NetID login, or borrow the physical books from the Libraries. For those without a UMass NetID or borrower's card, I recommend looking for these titles or other field guides in your area of interest at your local library.