You can invite new people to edit by clicking on the orange ... button and entering their email.
You can also view historic versions of the page from the ... button.
If you do not see the pencil or orange ... button, try adding /edit to the website address. For example if the address is https://example.com/foo then enter https://example.com/foo/edit and if the address is https://example.com/ enter https://example.com/edit. Also, if the address has # in it, remove the # and everything after it, for example https://example.com/#s=something becomes https://example.com/edit
There is no auto-save - you need to click the green accept (checkmark) button; you can also use the red reject (x) button to discard changes (the browser will warn you)
You can copy-paste images - they will be uploaded when you save the page; if images are big, pasting them can take a few seconds - just wait a moment after pasting. If you have pasted a few images, and click the green save (checkmark) button, the save will take a while, as the images are uploaded.
You can also insert new images in free-flow text sections by clicking the "Image" button; then click Upload (and wait a few seconds if nothing shows up); after selecting your image, click Upload again.
After inserting image you can (and should) resize it so it fits the screen.
You can drag around images in the main text. You can also drag around paragraphs (especially useful in various lists, like table of contents). To do so, click and hold for a second, then drag.
When editing, especially translating, links (or other formatted content like headings), to avoid losing formatting position the cursor in the middle of the link, type the new text for the link, and then remove the bits you don't need; eg. if you have link that says "Home", then move cursor say between "H" and "ome", type "Strona Domowa", getting "HStrona Domowaome" and remove the "H" and "ome".
Before a section of text is first translated, it will appear in the original language. As the original language is edited, it will keep changing in the translated sites. Once you edit the translated version in any way, it will stop being in sync with changes to the original language.
What constitutes a "section of text" depends on the particular website. If content is in some sort of box, then it's usually a separate section. Often though the main body of text is a single section.
There's a bottom editor section of the page, usually on blue background, which is visible only to editors. It lets you edit things like the title of the page that shows on the browser window bar, or description and keywords used by search engines.
You can replace images by clicking on the Edit images in the editor section. This replaces existing images and once you confirm you cannot undo easily (short of uploading the old picture again).
To add a new sub-page, first add a link to it - write the link text (eg. Sleeping hall), select it, click the "chain-link" button, and enter link, for example accomodation. There should be no spaces or special characters in the link. Letters, hyphens, underscores and numbers are OK.
Now, save and follow the link; on the not Not found page, click the link Create page (note to developers - this will clone _new.html file).
You can give an id to a section header or paragraph. To do that, edit the section header, and click the purple "H1", "H2" or similar at the bottom of the screen. In the dialog enter id as Name and something like my-section (no spaces!) as the Value. Once you do that, you can insert a link somewhere (using the chain icon) and use #my-section as the link value. You can also link to say transportation#my-section if the link is not in the current page.
For Vimeo, go to the video you want to insert, click the share icon, look for "Embed" section, find a link there that should read something like https://player.vimeo.com/video/123456789, copy it. In the editing interface press the "Video" icon, and enter this link. After inserting, resize by dragging upper left or right corner.
For YouTube it's similar - click share, then click Embed, and copy link from there. It should be something like https://www.youtube.com/embed/xyz123abcde