还是 is used to offer choices and it should be thought of as ‘(whether) . . . or . . .’.
Zhǔ rén ：Wǒ men yǒu kā fēi，yě yǒu chá；nǐ xiǎng hē kā fēi hái shì (hē )chá？
Host: We have coffee and we also have tea. Would you like to drink coffee or tea?
Kè rén：Wǒ xiǎng hē chá。
Guest: I would like to drink tea.
Sometimes, more than two options are offered; 还是 is used between the last two options.
Nǐ xǐ huān rì běn chē﹑měi guó chē hái shì dé guó chē？
Do you like Japanese cars, American cars or German cars?
 Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.