In summary, the directive states that no human may contact protected pre-contact worlds with evidence of sapient life or interfere in their natural development. Contact can only be made with a species who has developed Warp Drive, plus having the capacity to show tolerance of others as well as a healthy respect for their environment.
In the event of contact with a species that has developed the Warp Drive it is recommended that they are quietly studied from afar and if they meet the other requirements of contact, First Contact can be initiated.
This directive even applies to species like the Horuth who have been spacefaring for millions of years but have as of now not yet cracked FTL. The potential disaster in revealing the reality of FTL could cause an uproar in civilizations like theirs.
With the advent of multidimensional travel, the rules governing the Contact Directive needed to be expanded drastically, and now aside from the restriction concerning pre-warp civilizations, there is now a section concerning multidimensional civilizations, which basically expands the current restriction to that of multi-dimensional travelers.
A breach of either of these protocols could result in a court martial at least up to the complete destruction of the offending captain's DNA at worst.