In English, the article "the" is usually used when referring to a certain day. For example:

I will see you on the 3rd of January. (I will see you on January 3rd.)

When expressing the date of a certain day, the article " the" is usually required. However, when expressing the day of the week on a certain day, the article "the" can be omitted.

For example:

I will see you on Monday. (I will see you on Monday.)

In addition, when expressing the month to which a certain day belongs , usually without using the article "the". For example:

I will see you in January. (I will see you in January.

)