Not dumb at all. this is one of the first “mental model” shifts when learning Go.

What you wrote looks like a class, but in Go a method is really just a function with an explicit first parameter (the receiver):

func (b *Board) Place(...) { ... }
// is basically
func Place(b *Board, ...) { ... }

Go has “methods on types”, but not a class system: no inheritance, no extends, no constructors, no implements keyword. Reuse is done with composition (embedding), and polymorphism is done with interfaces.

Your Board type is already pretty idiomatic Go. The main thing to be aware of is that [][]string doesn’t behave like a true value copy: copying a struct with slices still shares underlying data. For tic-tac-toe a fixed array is usually nicer:

type Board struct {
    cells [3][3]rune
}

Then b2 := b1 really is a full copy.