I owned all of the Palladium Books RPG source books, Teenage Mutant Ninja Turtles & Other Strangeness being my first. Robotech was of the poorest quality and you should dismiss it in favor of Rifts.
I hope my simple answer will get you where you need to be. It is possible Robotech doesn't contain the information you desire to bridge the gaps in information. If that's the case, then nearly any of the other books will suffice to augment your knowledge of the rules. However, I believe that as long as your stats (Physical Strength, Physical Prowess, Mental Endurance, Mental Affinity, etc.), SDC/MDC (Structural Damage Capacity/Mega Damage Capacity), and others are all defined, and you have a character sheet, then the use of skills is simple.
A skill description should tell you what your base percentage chance of success is, which is further increased by accumulating a set number of percentage points per level of experience of the character. An example skill description is similar to this (credit here):
Mecha Electronics: First hand knowledge of the electrical systems built into RDF, REF and Southern Cross mecha. The character knows exactly how they interact with protoculture and the intricacies of Robotechnology. Other skills in electrical systems do not apply to mecha, making this an invaluable skill for repairing the famous war machines. Base Skill: 35% + 5% per level of experience.
When asked to perform a skill check by the GM, or when the GM allows a skill check upon request, a player rolls a set of percentile dice. Percentiles are simply represented by rolling a ten-sided die twice and taking the first roll to represent the number in the ten's place, and taking the second roll to represent the number in the one's place. If your roll is less than or equal to the required percentage, the skill use is a success. Using the example skill above, a 2nd level character has a 40% chance to modify, maintain, or repair Southern Cross mecha electronics. Rolling a 39%, or less, is a success. Rolling 40% or higher is a failure.
No skill can have a higher success chance than 98%, which is meant to represent the ubiquitous possibility of failure, no matter how skilled the performer.
Application of skills is largely up to the GM and the player, but should be covered in the skill description itself:
Prowl: This skill helps the character to move with stealth; quietly, slowly and carefully. Techniques include balance and footing, short steps and pacing, rifle positioning, prone positions for low visibility, and crawling. A failed Prowl roll means that the character has been seen or heard. If the Prowl is successful, then the character is not seen and may make a Sneak Attack. Base Skill: 46% + 8% per level of experience.
If a player told the GM that he wanted to crawl underneath a car to quietly avoid being detected by a security guard, then the GM could logically ask the player to perform a Prowl skill check.