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if is a macro — works as you'd expect, but case and cond are more idiomatic.

case matches a value against patterns:

case n do
    0 -> "zero"
    n when n > 0 -> "positive"
    _ -> "negative"
end

The _ is a catch-all. when clauses add guards.

cond is for arbitrary boolean conditions:

cond do
    n > 100 -> "large"
    n > 10 -> "medium"
    true -> "small"   # always-true catch-all
end

if/else for simple binary decisions:

result = if x > 0, do: "positive", else: "non-positive"

In Elixir, only false and nil are falsy. Everything else (including 0 and "") is truthy.