The place where you want to start when adding any sightings to eBird is Submit Observations, accessible as a tab at the top of any eBird page. Once you've gotten to that page, you'll be looking at the image shown here to the right – Where did you bird? This page is separated into two sections, the top one being "Choose from Your Locations", and the bottom being "Find it on a Map", with additional methods of selecting your location below that.
Choose From Your Locations is a method of quickly submitting sightings from a place that you've already eBirded, where Find it on a Map is how you add a new location that you have not eBirded. More details on both processes below.
Choose from Your LocationsThis section will appear once you've already submitted a checklist to eBird, and it becomes a dropdown list of every location that you've submitted to eBird anywhere in the world. By looking at this list, you can choose locations that you've already plotted on a map before, without having to go through the mapping process again. If you are birding a location you have not eBirded before, you must create a new location using Find it on a Map, not selecting or editing one from this list.
Find it on a MapThis is the primary way to add a new location to eBird. All you have to do is enter your county, state, province, or country in this box (e.g., "Essex"; or "England"; or "United Kingdom"), and then choose the option that appears in the dropdown menu, as shown to the right here. Make sure that you just enter the name of EITHER a county, state, province, or country – not both. For example, "Essex, England" won't return a result, but "Essex" shows the example that you see to the right here. If the list shown here is too long to see your correct entry, you are able to scroll down in the small window and access names that may not be visible on the first few displayed.
Once you choose a location, a Google Map will open, centered on the location that you chose using Find it on a Map, as shown to the right here. This map will have markers scattered across it, in both red and blue. The red markers are hotspots, and the blue markers are personal locations that you've already placed on the map, which are locations that only you can see as opposed to the hotspots that everyone can view.
You can choose either one of the previously existing spots, or you can click on the map to make a green marker appear, shown in the center here. This creates a new spot, which you can name on the right side of the page in the available box. Once you do that, you are taken to the effort page, where you can fill out your start time, duration, and the birds you saw! For a complete guide for entering data, see this article.