The Bill is now an Act. It may become law immediately after the President signs or there may be a clause or clauses in it which specify when it will come into effect. For example, some Acts contain a provision that they will come into effect within, say, one month of being signed. Sections may come into effect at different times. Sometimes there can be a very long delay in bringing sections into effect.
Subordinate legislation is a lesser form of legislation than Acts.
The most common is a Statutory Instrument. There must be specific power laid down in an Act in order to allow a Statutory Instrument to be effective. Usually an Act authorises a Minister to make Regulations dealing with details. The Act itself sets out the general law. The Statutory Instrument cannot deviate in any way from what is laid down in the Act - if they do, they are what is called ultra vires.