From what I remember, the front side (shown by the white circle rather than the coloured one) is what the card is considered in all zones unless it has come in to play as the reverse side. It's only when you play it that you can choose for it to come in to play as the reversed side.
They have been designed such that the reverse is always a land (much like the transform cards from Ixalan). The front sides vary between lands and spells, but for your example yes, the front side is the spell side.
It would trigger for yuriko and you can play it off Courser. Courser just lets you play lands from the top of your library, and if the top of your library is a MDFC, it has at least one land side and can therefore be played. Taken from the rulings:
"If an effect allows you to play a land or cast a spell from among a group of cards, you may play or cast a modal double-faced card with any face that fits the criteria of that effect."
They essentially work like other flip cards. They are the front side in all zones, and the front side is shown by the side with the white circle. The only real difference is the way in which they are "flipped". Because the reverse is always a land, you just have the choice to play it as such (and playing lands doesn't use the stack of course, so no
shenanigans there to be had). There are no additional clauses that need to be met like werewolves or meld cards or ixalan flip lands. Just your own choice.
Also, as an additional point, things like
expedition map can't go and fetch a spell/land to hand to then be played as a spell as it's still a spell and not a land while it's in your library.
EDIT
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Updated to display accurate information for future readers to save going down the thread. Originally I thought you couldn't play MDFCs off courser, but I looked in to it deeper and it turns out you can.