Ikkyo/Ikkajo, however you call it, is a way of breaking Uke's balance and controlling him by centering your movement on his elbow. You extend him with movement from the hips.
Moving close to Uke, support Uke's arm in front of you, holding at the elbow and wrist with both arms in Tegatana ("sword-hand" the not straight-not bent relaxed shape in the arm) then do not work the arms further. Uke must now be off balance (if not, your distance is wrong - move closer). Now move your body forwards from the hips, keeping your arms relaxed in front of you and in your center. This will apply Ikkajo/Ikkyo to Uke effortlessly and effectively.
The pin is by applying pressure to the elbow through the hand, but using lowering the hips to apply this pressure, not the shoulders or arms. The greater the angle between the arm and the torso, the more effective it is.
The one thing that my mentor told me that fits here is always "ELBOWS DOWN!" Keep the elbows pointing to the floor all the time.
Ask your instructor about this. As my collegues - ie: fellow Aikidoka - in Malaysia say: to learn from a book is to learn from the devil. IE: You need a teacher!