The Windows part of this sharing is extremely simple. For instance, if you use Dropbox, simply keep your database file (the one with the .kdbx extension) in your Dropbox folder.
Things are a little more complicated in Android, which is why you want Keepass2Android to help you smooth them out. The first time you launch the app, tap the Open file button. You'll find Dropbox (and other cloud options) on the list. It's all very simple from there.
But Keepass2Android has one major flaw. Copying usernames and passwords from the app and pasting them elsewhere isn't as intuitive as it should be. Here's what to do:
After you've opened Keepass2Android, typed in the master password, and gone to the item you need, tap and hold on the User Name until all or part of it is selected. If only part of the name is selected, use the selection handles to select the entire name. Then tap the Copy icon in the upper-right corner.
Go to the app where you want to paste the text--Twitter, Chrome, or whatever. Tap and hold on the appropriate field until the Paste option pops up. Tap that.
For the password, tap the eye icon near the top-right corner to make the password visible. Then follow the same directions as above.