In 5th Edition D&D, a Ritual spell means the spell may be cast as a ritual, not that it must be cast as a Ritual.
From the Player's Handbook, regarding Ritual Spellcasting:
Certain spells have a special tag: ritual. Such a spell can be cast following the normal rules for spellcasting, or the spell can be cast as a ritual. The ritual version of a spell takes 10 minutes longer to cast than normal.
It also doesn't expend a spell slot, which means the ritual version of a spell can't be cast at a higher level.
To cast a spell as a ritual, a spellcaster must have a feature that grants the ability to do so. The cleric and the druid, for example, have such a feature. The caster must also have the spell prepared or on his or her list of spells known, unless the character's ritual feature specifies otherwise, as the wizard's does.
So if you get the Find Familiar spell through Magic Initiate, but don't have the ability to perform Ritual Casting, you are still able to perform the spell as normal. You simply won't be able to cast it using the Ritual Spellcasting rules.