I would need more information, but in general, what that means is the following: When you have a minor child, the court always retains jurisdiction to order support for that child even if the Court declines to make an actual order at that time. The Court's ongoing jurisdiction to award child support is set forth in California Family Code Section 3901 which states as follows:
3901. (a) The duty of support imposed by Section 3900 continues as
to an unmarried child who has attained the age of 18 years, is a
full-time high school student, and who is not self-supporting, until
the time the child completes the 12th grade or attains the age of 19
years, whichever occurs first.
(b) Nothing in this section limits a parent's ability to agree to
provide additional support or the court's power to inquire whether an
agreement to provide additional support has been made.
It is most likely that the Court did not have enough information to issue an appropriate child support order. If you desire child support, my suggestion is to 1) hire counsel, or 2) go to the local child support agency; or 3) go to the family law facilitator's office which is located in your local courthouse.
Generally speaking, I see a reservation for support when support -- whether it is child support or spousal support --is set at zero. This empowers the Court to make orders at a later date if and when necessary.
Reserves jurisdiction means that the court retains the right to determine the issue (in your case-child support) at a later date. It means that you or your ex can file applications in the court to modify the child support order (if already passed) or request orders for child support in the future. The court generally reserves jurisdiction over child support if no child support has previously been ordered because this issue cannot be waived.
The answer above should not be relied upon as legal advice. The information provided above is based on insufficient facts and only speaks to a general opinion based on those insufficient facts. No warranty is provided that the answer is correct. No attorney-client relationship has been formed with me until a signed written contract is complete. For an official opinion, it is advised you seek legal counsel.