How does a current flow in here if this is not a loop?
This is a common way to simplify circuit diagrams.  The &quot;+10V&quot; label and little arrow mean that that point on the circuit is connected to something (such as a battery or power supply) which is also connected to ground (the symbol at the bottom).
The three diagrams below mean exactly the same thing.



simulate this circuit &ndash; Schematic created using CircuitLab
In your case, the textbook has gone a step further and missed out the battery entirely. Probably becasue it doesn't matter for the discussion at hand.