Number + 期 + Noun
期 (qī) is a measure word (classifier) used for scheduled installments, issues of a publication, or episodes of a program. For example, 一期节目 means "one episode of a program" and 第三期杂志 means "the third issue of a magazine." It emphasizes the sequential or periodic nature of the item.
这是我们杂志的第一期,欢迎大家订阅。
Zhè shì wǒmen zázhì de dì yī qī, huānyíng dàjiā dìngyuè.
This is the first issue of our magazine; welcome everyone to subscribe.
这期节目请到了一位著名的科学家。
Zhè qī jiémù qǐng dào le yī wèi zhùmíng de kēxuéjiā.
This episode of the show has invited a famous scientist.
培训班一共有四期,每期两个星期。
Péixùn bān yīgòng yǒu sì qī, měi qī liǎng gè xīngqī.
The training course has four sessions in total, each lasting two weeks.