The meditation icon is the center of that icon with swords one sword on top and one on bottom with a center icon and left being the signs cant remember whats on the right. soon enough after you see the next place/ battle there will be a fine spot to meditate, but I suspect you could do it now since it gives you the option to drink a potion.
were you wanting to level your character? drink a potion/ make more potions? check your stats? just curious.
edit: semi- spoilers
anyway, yes you can meditate in the prologue, there will be many houses to look inside very soon and i meditated in some of those. There will be an underground area that I was able to meditate there as well soon after. so there will be places that will let you.
Ah that explains it. I was trying to click on the word "meditate" insted of the centre. Many thanks.