In some cases, when adventuring, a party may need to move silently. In some cases, a single character may need to make a check - such as when one character is leading the party in the wilderness. In other cases, where it is unreasonable for only a single partty member to make a check, a group check is called for instead.

When a group check is made, if at least half the party succeeds, the group as a whole succeeds. If more than half the party fails, the group as a whole also fails.

For example, when the party needs to move stealthily, a group check may be used, with the more successful party members, aiding the less stealthy.

 

In some cases, a Group check may still end up as a Pass or Fail, in some cases where a party member in full plate fails their Stealth check terribly, this can have a full adverse affect on the party's stealth capability.

 

In cases where a party member is unable to succeed on a check, but could have reasonably passed with assistance from party members, if the aid is roleplayed well enough, the DM may allow it.

There may be times when a character may only perform a check if they have proficiency. One such case would be identifying an enemy creature.

For example, to identify a beast in combat, one may be allowed to make a Nature(Wisdom) check to identify the creature, but only if they have proficiency. This represents a creature's effective knowledge of such a creature. 

When you fail a skill check, you can attempt to re-do the check. Doing so allows you to redo the check at disadvantage.
Be aware however, if you fail a second time, you may experience mishaps. A second attempt picking a lock may cost time or fully jam the locking mechanism. Failing a seond time to disarm a trap may trigger it.

In some cases, the dice are unforgiving. In this case, you could "Take 10". In this case, as long as the task is within your character's ability, you can succeed at the task, but it takes 10 times the regular length of time. As an example, a trap that takes 1 minute to disarm properly would take you 10 minutes instead. However, do remember that no amount of "Taking Ten" will turn an impossible task into a success.

 

Example:

Phoenix Hofstedder has a climb speed of 30 and is trying to scale a 300 foot cliff. With successful skill checks, this would take him 1 minute to successfully climb, But Phoenix worries about his athletic ability to scale such a steep cliff, taking a total of 10 minutes to climb the cliffface.