In English most words can be multiple parts of speech. While "open" can be a verb describing the action, it can also be an adjective describing the state of the door. "Watch" can be a verb, or it can be a noun, like Abigail has pointed out. You will see this with many English words. "Book" can be a physical object or the act of scheduling something. "I read a book." "I booked a flight." "Fly" can be an annoying insect or it can be the action of moving through the sky. Side note on slang: because so many words in English can be multiple parts of speech and because English doesn't have specific endings or forms for the different parts of speech, English slang will give words even more ways to behave. Even though "English" is a noun or an adjective usually, you may hear people using it as a verb "I can't English well today." (Meaning, I am having trouble speaking English today.) While that use is not technically correct, you may see native speakers doing so in informal contexts. I wouldn't recommend learning to do this yourself until you are really comfortable with English, but I wanted to give you warning that you might see others doing it.

'Yanked open' is a combination of a conjugated verb (yanked) and an adjective (open). We use this structure when the result of the action changes the state of the object. In grammatical terms, 'yank open' is similar to saying 'shoot dead' or 'cut short'. 'Stand watch' is a combination of verb and a noun. 'Watch' is a noun in this context. You can also 'keep watch'.

In the first two sentences, "open" is a preposition, not a verb. In the third sentence, "watch" is actually being used as a noun, similar to the word "surveillance." You're right that normally, for two verbs to be used together, the second would have to be an infinitive with "to," but these sentences only have one verb.