There are countless historical and modern texts that will be useful for anyone new to Hellenic Polytheism. We can't possibly list all of them, but I'm going to attempt to link what I believe to be the most useful for beginners.
Each of these resources can be found on Theoi.com. This website is commonly recommended across Hellenic Polytheist circles because it contains so much useful information.
Each of these links is to a historical text from Theoi's pretty extensive Library. These texts were chosen based on personal experience and based on what I see most recommended in various Hellenic Polytheist spaces online. Each of these texts is very useful, but please don't limit yourself. Read and learn as much as you can.
Theoi also has individual pages for a lot of the Greek gods. Here you can find them compiled and easily accessible.
Social media can be one of the most useful or harmful things for beginners. You have to know what to look for to find healthy community and avoid misinformation.
Community can be so important for a lot of people.
Here are some groups that might be useful for you.
This community is a great tool for a lot of people, but is not exempt from internet drama. Most people here are friendly, but there is definitely some uncomfortable discourse and common disagreements, as well as a lot of of people who are new to the religion. Take everything you see on this community with a grain of salt. A good thing about this community is it is very active.
An old community that was abandoned, but a friend claimed and is trying to restore so there are multiple safe Hellenic communities. This one isn't currently very active, if one would consider it active at all, but the moderators are amazing.
A social and friendly discord server run by a friend. It is targeted toward Hellenic Polytheists, but we are open to members of all religions and have a diverse community.
Hellenic Polytheism Facebook Group
A friendly private facebook group with some wonderful people. Community chats are pretty active and its a good place to meet friends and share your experiences. People are very gentle with beginners here and good at answering questions.
Here are a few other resources that might be useful.
Moocs
Many colleges have open courses, often for free online. Coursera has a few courses that may be helpful, including but not limited to:
Youtube
Overly Sarcastic Productions (For mythology)
Calendar and Festivals
Attic Calendar Wikipedia Page (For help understanding how the attic calendar works. Wikipedia isn't perfect, but is definitely useful.