go to a bar
The Spanish phrase 'ir a un bar' translates to 'go to a bar' in English. It is composed of 'ir' which means 'to go', 'a' a preposition equivalent to 'to' in English, 'un' which translates to 'a', and 'bar' which is the same in both languages. So, when you say 'ir a un bar', you are basically saying you are going or want to go to a bar.
This Friday we are going to go to a bar with friends.
In this example, the speaker is indicating that they have plans to go to a bar with friends on Friday.
Would you like to go to a bar after work?
Here, the speaker is inviting someone to join them at a bar after their workday is over.
She decided to go to a bar to celebrate her birthday.
In this phrase, it is mentioned that a woman has chosen to celebrate her birthday at a bar.