Questions & Answers about Сайт долго загружается, поэтому я пока пью чай.
Загружается is from загружаться and means is loading.
The ending -ся often makes a verb:
- reflexive,
- passive-like,
- or intransitive.
Here it gives the idea that the site is loading itself / is being loaded, which is the natural Russian way to say the site is loading.
Compare:
- Я загружаю сайт = I am loading the site
- Сайт загружается = The site is loading
So in this sentence, сайт is the thing undergoing the process.
In Russian, the present tense of an imperfective verb is exactly what you use for an action in progress.
So:
- Сайт загружается = The site is loading
- Я пью чай = I am drinking tea
Russian does not need a separate am/is/are + -ing form the way English does. The simple present form can express an ongoing action when the context makes that clear.