Where do I put the server.properties file?

Upload it to your server's root folder — the same directory as server.jar and eula.txt — replacing the existing server.properties file, then restart the server for changes to apply.

Do I need to restart the server after changing server.properties?

Yes. server.properties is only read on startup, so a full restart (not just a reload) is required for any change to take effect.

What does view-distance actually control?

How many chunks around each player get sent to their client and kept loaded. Higher values look better but cost more RAM and CPU per player — 10 is the vanilla default and a safe baseline for most servers.

Minecraft Server Properties Generator — server.properties Builder

What is server.properties?

server.properties is the plain-text config file that controls almost everything about how your Minecraft Java Edition server behaves — difficulty, gamemode, whitelist, view distance, RCON access and dozens of other settings. It sits in your server's root folder and is only read once, at startup.

Settings worth double-checking

online-mode — leave this true unless you specifically run an offline/cracked server. Turning it off on a public server lets anyone connect with any username.
view-distance and simulation-distance — the two biggest levers for RAM and CPU usage per player. Drop these first if you're short on either.
enable-rcon — only turn this on if you're actually using RCON, and always set a strong rcon.password. An open RCON port with a weak password is a common way servers get compromised.
white-list — combine with enforce-whitelist if you want changes to the whitelist to kick already-connected players immediately instead of on next join.

After you upload it

Changes to server.properties only take effect after a full restart. If your server won't come back up after editing, check the console log first — a malformed value (like text in a number field) is the most common cause. Not sure what RAM or Java version your server needs in the first place? Try the RAM calculator or the Java version checker.