The daily login bonus is a window that appears on your screen when you first log in, along with various other windows, such as the news screen and various ruby offers if they are running.
To the right you see my (IaLL/kuku9999) login bonus. The person who wants you to do the robber baron tasks tells you certain missions to do.
There are 4 levels of daily bonuses that you may receive. You may be asked to do the following, make an item in the smithy, attack an RBC, collect taxes, send resources to another player, spy, spend rubies in some way, and collect food from your citizens (does NOT matter if it is in an outpost or in another kingdom). If you complete all 12 before time runs out, you get 100 rubies.
Rewards vary by level and day as well, with time skips, powerful troops (such as Veteran troops or travelling Knights), tools, and also resources.
The tasks have names, such as "Dust and Sand", "Ice and Snow", as well as "Small Gifts".
These daily tasks are good if you need time skips to repair/upgrade/build items, as they are the easiest way to get them.