Wasp/hornet or bee?
We get this question a dozen times a day, please read through for a quick guide on differences, or flip through the slides for commonly submitted species. Pictures are largely taken from Bugguide with a full list of sources by slide at the end of this post, I assume that they are fine to use for free educational purposes but if the photographer would like me to remove their picture, please reach out to me so I can act accordingly.
To begin with, "wasp" is not a word to mean "stripe-y flying thing" but rather is a massive umbrella term that covers hundreds of thousands of species worldwide, all of which belong under the taxonomic suborder Apocrita. Apocrita contains many subgroups (families, tribes, etc.) of different types of wasp, and among those subgroups are Formicidae and Anthophila, which are the ants and bees, respectively. That's right, ants and bees are kind of just weird wasps! We consider them separate groups though, so let's say "wasp" means any species in Apocrita, excluding the ants and bees.
What separates wasp from bee then? Are there specific physical differences to look for? The unfortunate answer is no, or at least nothing that can be seen by a regular person taking pictures with a smartphone. There is just so much variation within Anthophila and Apocrita that we can't easily apply any single rule without adding on a laundry list of exceptions. Instead of hard rules, let's use the key phrase "tends to": bees *tend to* be fuzzier, wasps *tend to* be slimmer. Bees tend to be seen carrying pollen, but only females work to provision the nest and even then some species don't collect pollen at all (there are even bees that feed on meat! Known as vulture bees, Trigona sp. of South America). Conversely the majority of wasps tend to provision nests with hunted or scavenged protein but there are also wasps who feed their larvae pollen and nectar (pollen wasps in subfamily Masarinae, funnily enough in the same family as the predatory hornets and yellowjackets).
At the end of the day the only way to be confident is to become familiar with the species in your area! Use iNaturalist to get a general sense of what's in your area, and use reliable resources like Bugguide to check for more details on particular groups and species. It can get tricky sometimes so you're always welcome to post in one of the various bug identification subreddits. Mod Commercial Sail is also over at r/bugidentification if you'd like help from them there!
Sources
Cover: https://www.bugguide.net/node/view/1507885/bgimage
https://www.bugguide.net/node/view/1516079
https://www.bugguide.net/node/view/834403/bgimage
Honeybees: https://www.bugguide.net/node/view/2184472/bgimage
https://www.bugguide.net/node/view/1797962
https://www.bugguide.net/images/cache/YHP/HHR/YHPHHR2HCHXLEZKL5ZSL4ZRLGZ7LGZRLGZSL8ZMLNZ9HFH4LWZ8LAZ4L6Z5H2Z8HLR9HJHIL5ZHLUZWHHR6HAZWHJH.jpg
Bumbles: https://www.bugguide.net/node/view/2083857/bgimage
https://www.bugguide.net/node/view/2461027/bgimage
https://www.bugguide.net/node/view/1715867
Carpenters: https://www.bugguide.net/node/view/1580663/bgimage
https://www.bugguide.net/node/view/97339/bgimage
https://www.bugguide.net/node/view/2307575/bgimage
Yellowjackets: https://www.bugguide.net/node/view/1832507/bgimage https://www.bugguide.net/node/view/1516079
https://www.bugguide.net/node/view/855086
Paper wasps: https://www.bugguide.net/node/view/2476447/bgimage
https://www.bugguide.net/node/view/1423151/bgimage
https://www.bugguide.net/node/view/2473595/bgimage
True hornets: https://www.bugguide.net/node/view/834403/bgimage
https://www.inaturalist.org/observations/66003667
Vespa velutina: https://bygl.osu.edu/node/2321