When to use "just" in a sentence?

Just is most commonly used as an adverb together with the present perfect tense. In this context, just means ‘a short time ago’, and is positioned between the auxiliary verb (had/ have/has) and the past participle.

For example:

• I’ve just spoken to John.

• Have you seen what’s just happened to the share price?

• They had just finished their dinner when the phone rang.

Just can also be used in place of the word "only":

• Can I have just a little bit of cake, please?

• That's just an excuse.

Although it is now old-fashioned, just can be used as a noun, relating to the concept of justice and standing in for 'right' or 'correct':

• Given the severity of the crime, life imprisonment was just.

• Her charity raises money for a just cause.

Finally, just is used in a wide variety of informal phrases:

• just a minute = wait
• just about = nearly
• just as well = for the best
• just help yourselves = go ahead
• just so = neat and tidy; precise