additonal animal companion feat from SRD tripod machine

[Malleus Maleficarum]

Prerequisite: Cha 13, ability to have an animal companion, effective druid level 4+ for purposes of
having an animal companion

Benefit: You gain an additional animal companion. Your effective druid level for the purposes of the second animal companion is your normal level -3.

Special: You can take this feat multiple times, each time gaining an additional animal companion.

Okay so my question refers to the prerequisite.

Does this mean I need to be druid level 4? How do I get my effective druid level 4 levels higher than I already am? I am very confused on this matter. Since the feat boon companion only makes you a druid of your current level (ie meant for multiclassing). What's going on here. Can someone explain?
What way can I achieve druid level +4?

[Weirdo]

You need to be (effective) druid level 4 or higher. So at least 4 druid levels (probably 5, since that's when you get your feat), or 7 ranger levels, or 4 ranger levels with Boon Companion.