Learn Spanish (Latin America): Mañana vamos a viajar, hay que descansar. - Tomorrow we are going to travel, we have to rest.

This is because of hay que, which means 'one must' or 'it is necessary to.' It is an impersonal phrase, meaning it does not specify exactly who has to do the action. However, based on the context of the first part of the sentence (vamos a viajar - we are going to travel), we naturally understand that 'we' are the ones who need to rest.

What is the exact difference between hay que descansar and tenemos que descansar here?

If you said tenemos que descansar, you are specifically saying 'we have to rest.' Using hay que descansar is a bit more general, literally meaning 'it is necessary to rest.' In everyday Spanish, both are perfectly natural and often used interchangeably when the context already makes it obvious who needs to do the action.

Why is the verb descansar (to rest) left in its infinitive form instead of being conjugated?

After the fixed phrase hay que, you always use the infinitive (the dictionary form ending in -ar, -er, or -ir) of the action verb. This is an unbreakable rule! So it is always hay que descansar, never hay que descansamos.

Why use vamos a viajar instead of a future-tense word like viajaremos?