No worries.
1. Look at the very top right of the Astrobin website, to the right of the gold "gift" icon, see the orange icon with an arrow pointing up from a short horizontal line? When you hover over it it says "upload". That's your image uploader
(I meant uploader before, not publisher, but they sort of mean the same thing, sorry)
2. When you go to the uploader, you'll see a thin box with "Title" to the top left of it, that's where you write the name of your image. For example, if you took a picture of the North American nebula you would usually type "The North American Nebula" in the "Title" box. It'll be the name of the image that everyone will see when you publish the image. No need to name your image "Essay".
3. You'll also see a large box, a really large box that says "DROP FILE HERE OR CLICK TO BROWSE", when you click it you will be directed to your own files on your device, that's where you get the image to publish. The file needs to be on your device, not online, if it's online then you need to download it to your device.
Keep in mind that whatever you do with the uploader, even if you upload an image, no one will see it unless you want. It's automatically in a "staging area".
4. After passing those steps and pressing the orange "Upload" button, you will be directed to a page containing your last steps. You'll see Basic information, Content*, Thumbnail, Watermark, Equipment, Acquisition, and Settings. Start with Basic information.
5. Let's go from top to bottom on every step. Keep the title you already wrote or modify it in the TITLE box. Write a description of your image if you want. Skip collaborators, that's for if you worked with another person for your acquisition. Link is also not necessary, both Link boxes, skip those.
6. Next, move to Content. Specify your Acquisition type in the box, your Subject type and your Data source. Locations are not necessary, but you can provide it if you want. Skip "Groups" unless you have joined a group and want to submit the image to that group.
7. Move to Thumbnail, select the area of your image that will appear (if you submit the image) as a thumbnail in the Astrobin gallery. Skip sharpening, it doesn't help.
8. Move to Equipment, all this is optional, but you can also specify what equipment you used for the image. Everyone can see what equipment you claim to have used for your image when you publicly upload your image.
9. Move to Acquisition, press "add session". You will be asked 4 things, Date of your acquisition (optional), Filter used for the acquisition (optional), Number of subs used for the session (necessary), and duration of every sub for the session (necessary). For example, if you used an H-alpha filter for six 300 second subs, you would put that for one session, and if you used an OIII filter for seven 200 second subs, you would add another session (just press "add session" again). All this will be shown with your image when you upload your image.
10. Move to Settings, keep License at none (unless you bought a license or something, I think it costs money, it's against image thieves, but Astrobin is secure enough for a beginner). For "Mouse hover image" select Plate-solution annotations; this will show the scientific designations of objects in your image when you hover with your mouse cursor; this will not work if you don't have an Astrobin subscription.
Skip "Key/value tags", I don't know what that is.
Keep "Allow full-size display" at default (which is "everybody")
Keep "Display download menu" at default (which is "Me only") unless you want to allow people to download your image (I think)
For "Allow comments", that's for whether you want to allow people to comment on your image.
11. Listen carefully, look to the bottom of the page, you'll see an orange button that says "Save...". Click it, and press "Save and proceed to image". Now you are in the "staging area" (which means only you can see it).
All you have to do now is check on everything about the image and the details, see if you like it, and press the orange button that says, "Promote to public area". And that's it, you published the image, publically...
I hope I made myself clear. Feel free to ask any questions.