From what I read, the establishment clause is a type of law put into place which gives a citizen religious freedom. In order to do so, the establishment clause makes it unconstitutional (illegal) for a state to have a preferred treatment of a religion. What this means is that the state can not officially impose rules that would force citizens to conform to a religion because doing so would strip away the freedom of choice that a person has with their religion. The Lemon test can be seen as an extension of this clause because it is a checklist of restrictions that a law must follow to be deemed constitutional. The lemon test aims to remove incentives attached to religion that would make it favorable to be apart of a certain religion, and disadvantageous for others. They do this through the 3 rules of not entangling government with religion, neither promoting or stopping religious practice, and by requiring a non-religious justification for the law.
Burning the US flag is protected by the constitution as it is considered a form of speech through its message. Because the message of burning the flag does not cross the boundaries of obscenity, the symbolic action of burning a flag can only be viewed as a message from the person burning the flag. In the case of Texas v. Johnson, they found the burning of the flag to be a form of symbolic speech and therefore a protected right under the 1st amendment.
When a person claims, “I’m taking the fifth” it is a display of them using their fifth amendment rights which gives them to ability to withhold answering and fiving evidence of themselves to the court. This allows the person to keep their information to themselves and protect against self-discrimination.