Okizeme is pressure against a grounded opponent. Generally, the grounded player (defender) wants to get up safely while disrupting the opponent's pressure, and the standing player (attacker) wants to get free damage while they can't guard or act.
Responding to okizeme
Much like pressure in general, what options to chooses depends on a lot of situational factors: the grounded position, whether a tech recovery is possible, the frame advantage, the matchup, spacing, wall position, and life lead.
For the defender, tech rolls when possible are the most reliable choice. However, because they both take a long time and have a long period where you can guard but not act, this risks giving your opponent a free mixup where you can't low parry.
To avoid eating such a strong mixup, we can instead stay down to force them to use ground hitting moves. This achieves two things: if the attacker refuses to add ground hitting moves to their pressure, they'll likely whiff something that you can whiff punish with a wake-up kick; and if the attacker does add ground hitting moves, when we do tech the mixup isn't as strong.
If we choose to stay down and wait and the opponent also chooses a passive option, the safest way to get up is quickstand, not b getup. Quickstand recovers faster, but more importantly threatens a wake-up kick while recovering. Without this threat, the opponent can wait and react to you getting up and then safely go for a big mixup while you can't act. Big exception when in the FDFA position, where B getup can guard much quicker and where the distance created is substantial enough that you aren't as likely to eat a big mixup.
In many cases, ground hitting moves are too slow to beat wake-up kicks. All the options here are worth using on occasion, but our biggest threat is the wake-up low, which is always a counter hit launcher. From FDFA, wake-up kicks are much slower, so we mainly use while standing kicks from quickstand instead.
Side roll is mainly useful in situations where a tech roll isn't possible to avoid a strong, linear ground hitting move. The main issue with side roll in general is that it extends your hurtbox, making more moves hit you, and because it takes a while it prevents you whiff punishing anything.