2 sentences for 其一 (qí​yī — firstly)

1. 理由有二：其一，时间紧迫；其二，人手不足。

   lǐ​yóu yǒu èr: qí​yī, shí​jiān jǐn​pò; qí'èr, rén​shǒu bù​zú.

   There are two reasons: first, time is tight; second, there is a lack of manpower.

   Source: Dong Chinese Dictionary

2. 学习汉语分为两步，其一是多听，其二则是多说。

   xué​xí Hàn​yǔ fēn​wéi liǎng bù, qí​yī shì duō tīng, qí'èr zé shì duō shuō.

   Learning Chinese consists of two steps: first, to listen more, and second, to speak more.

   Source: Dong Chinese Dictionary