Please point to a simple database listing predicted brightess of objects with well-know periods. This would be useful for beginners to validate our observations. I found some links here, but none are simple enough for this beginner.
I.e., object x will be at max on these dates: <list>
Since you asked for a database - I think the "Variable Star Index" VSX would be a good starting point
(you can find the link on the AAVSO homepage under the tab "Variable Stars")
1. Click on "Search", and the "Search" window will open.
2. Fill the "Name" field with your variable star, e.g. "R Leo".
3. Press "Search" on the bottom.
A window "Latest Details" will open with data for your chosen star. E.g., for R Leo you will find a "Mag. range" of 4.4 - 11.3 V and a "Period" of 309.95 d. In the line "Epoch" you can click on "Ephemeris". This should open a window with a list of date/time values of former and predictions for the next minima.
Now, to get better values for magnitude(s) at specific times - that you might want to compare with your own observations - you probably should familiarize yourself with
Light Curve Generator, (see under the tab "Data", then "Data Access")
Again, fill in your "StarName", and "Send" your request. On the appearing light curve page you can choose different filters, date ranges etc. Play around with those parameters... :)