What are the differences between an LDO and a Restricted line officer? Also, how do you become a restricted line officer?

Unrestricted Line Officer (URL) = Aviation, Surface Warfare, Submarine / Nuclear, Naval Special Warfare and Explosive Ordnance Disposal.

Restricted Line Officer (RL) = Aerospace Engineering Duty, Aviation Maintenance Duty, Cyber Warfare Engineering, Engineering Duty, Foreign Area, Human Resources, Information Professional, Cryptologic Warfare, Intelligence, Public Affairs, Oceanography and Permanent Military Professor.

Limited Duty Officer (LDO) = between 8-14 years enlisted time in service. Does not need a degree to commission, but must be at least E6 with 1 year time in grade and pass the E7 exam to be eligible to apply. LDOs serve in leadership roles as technical managers in broad fields related to their enlisted ratings. Some LDO (and CWO) designators have a RL or staff designator that roughly does the same thing (supply corps LDO vs supply corps RL // Aviation Maintenance Duty Officer RL vs Aviation Maintenance LDO) to point out two. LDOs will never command a ship or squadron, but may command a training unit or base.

ROTC and USNA will both commission into the RL, as will OCS. It just depends on what you qualify for, what is available, and what you want to do.

Here is the officer community manager page for the Navy:
https://www.public.navy.mil/bupers-npc/officer/communitymanagers/active/Pages/default2.aspx

LDO does not require a bachelors degree, but does require significant technical expertise and experience, similar to the warrant officer program, both fall under the same in-service recruiting program. It's something that you can qualify for after at least 8 years in a list of specific rates in the Navy.

Restricted Line Officer requires a degree and a commissioning source, and as the name implies, restricts that officer to that branch (aviator, engineering, etc).