This is a matter regulated at the state level (with a generic guide here), so I'll pick a random state, Washington. RCW.2.48.180(2) says that
The following constitutes unlawful practice of law:
(a) A nonlawyer
practices law, or holds himself or herself out as entitled to practice
(irrelevant clauses pertaining to the business of running a law firm suppressed). In telling you this, I am giving you legal information, not advice. I also have the opinion that the laws of Washington do not forbid me from saying "I don't think you will get in trouble for saying what you think the law says". If I were to say "Based on my years of experience in contract litigation, I would say that you would be legally safe if you did X", then I would probably get in trouble. Obviously, appearing in court as someone's attorney is a violation, as is opening a business that claims to be a "law firm" or "legal office".
There are also court rules, and in Washington rule GR 24(d) says "Nothing in this rule shall affect the ability of a person or entity to provide information of a general nature about the law and legal procedures to members of the public"