When you open the folder, you have to open the versions folder to find all the old versions. When you enable the snapshots button, you can play the latest versions released and put those versions in your Minecraft game folder.

If you are using a modded version, you can check or uncheck the modded profiles in Minecraft, as shown in the image below. When the optifine installs in this Launcher, it patches Minecraft itself, and it is not a good practice to do it. If you install optifine, it will create its profile in the Launcher, but it will not run as a mod. But it will be tough to manage the profiles because this Launcher depends on your system Minecraft game folder, and to find all the profiles you created, you have to open your game folder, and there you will find all of your profiles.

If you want to play the modded version, you have to install Forge as a profile to make the profile in the Launcher and then add mods to that. If you need to play Minecraft, you have to download the Launcher, and it will automatically install the Java and verify it as well in the Launcher. You cannot use this launcher for the modded version because it has its java version inside, so you cannot use the system’s java.

Start old minecraft launcher