Juokse = Run (as in a command), Juoksennella = to run around aimlessly.
Juoksentelisin = I would run around aimlessly (-isin means that we're talking about "I" here, and it also includes the "would" in the -tel- part combined with the -isin.) ((it would be "juoksentelen" if the person was doing it right now))
Juoksentelisinko = Would I run around aimlessly? (-ko signifies that the person is not sure and asks a question, "Would I?"
Juoksentelisinkohan = I wonder if I should run around aimlessly? (it looks unreal that a simple -han could add this much stuff but yeah, it does. The word can also mean "I wonder if I WOULD run around aimlessly?")
In a same fashion you can say, for example, "rakentelisinkohan?". (Rakentaa = to build. Rakentelisinkohan = I wonder if I should/would build (something) randomly/aimlessly?"
And that's Finnish for you. Don't ask how native Finns learn that shit, I'm not even sure myself.