What is the difference between a VAR check, a VAR-only review and an on-field review?

• Check: the VAR automatically checks the footage of every potential or actual goal, penalty, direct red card or mistaken identity incident. If there is no clear and obvious error, there is usually no need to speak to the referee (a "silent check"). When a restart is delayed for a check, the referee holds a finger to the earpiece and extends the other arm.
• Review: if the check shows a probable clear and obvious error or serious missed incident, the referee decides whether to start a review. If play has not already stopped, the referee stops it when the ball is next in a neutral zone or situation and shows the "TV signal".
• VAR-only review: the referee decides using their own perception and the VAR's information. This is usually appropriate for factual decisions such as offside position, point of contact or whether the offence was inside the penalty area.
• On-field review (OFR): the referee goes to the referee review area to watch the replay. This is appropriate for subjective decisions such as the intensity of a foul challenge or handball considerations.

Players and team officials who excessively show the TV signal or enter the review area are cautioned. Anyone who enters the video operation room is sent off.

Source: https://www.theifab.com/laws/latest/video-assistant-referee-var-protocol/