This question has been asked multiple times and in multiple forms. Here is another one and another one.
While fade-out content, arrows, truncation etc. are (im)possible solutions, they are just plasters that can quickly come off. The only thing that really works, which is much harder to get right, is a good content strategy. When done right, users will have the urge to scroll. But you can give this "urge" a push with some good design choices:
- If you have a footer, don't make it float at the bottom of the screen. Show it at the bottom of the page so it can only be reached by scrolling. If you don't like this, consider a different strategy for its contents and have no footer at all.
- Use consistent containers for content with enough padding and margin and a background or border with enough contrast to make it easy to distinguish the end of the container. If the content of that container looks complete at the end of the screen (a line of text that fits perfectly on the screen) the container shows that it is not the end.
- Show a compact table of contents of the page. You can place this at the top of the page and make the items link to that part of the page. This should also be considered for mobile screen sizes but that depends on how much space it takes. In combination with the previous points this might be not necessary or can for example be omitted on mobile devices only.