Are long scrolling websites good?
Long scroll websites are great for certain types of content but can present a huge UX failure with other types. On the whole, task and goal-oriented sites don't benefit from infinite scroll designs (e.g., eCommerce sites and tutorial or other educational sites where users want to see definite progress).
How do you indicate something is scrollable?
Indicate content overflow by cutting off grid tiles. Or alternatively you can directly ask users to scroll. A subtle cue, such as an arrow pointing off-screen or a text “scroll down,” can inform users that most of the content will be laid out linearly.