The video below shows the technique Ikkyo (jap. "first teaching") aka Ikkajo ("first principle") aka Ude-osae ("forearm pin") in some usual forms.
The focus here is in tori's hand movements: forearm rotation and changing wrist position.
Aikido is practiced with these roles:
Tori = the one who is performing the technique (aka "Nage" or "Shite").
Uke = the one who is receiving the technique (aka "Aite").
Omote = front of uke.
Ura = behind uke.
Irimi = to enter (move ki forward).
Tenkan = to turn (change direction of ki).