Foot work in aikido is very hard to describe, but I will try.
Aikido footwork- the basics
Kamae (basic stance)- the main things to learn with your basic stance is always to maintain balance, have the hands, hips and feet at the centerline of the body, keep correct posture ( shoulders back and relaxed back straight, hands at the center as if holding a sword, and fingers separated but extended).
Your feet are both pointed forward but slightly out , shoulder width apart, your hara (center two inches below the navel) is always pointed at your uke. Your knees are bent (yoshinkan differs in that the back leg is extended) with a 60-40 weight distribution, 60 being on the forward foot.
Hips are always forward, upper body is extended so that it is slightly forward, neck is also straight. Your hands are forward (like I mentioned "holding a sword") but relaxed so that they are not rigid or over extended, much like when you chop wood..
This is the basic stance.
Irimi
Irimi or entering is the signature of aikido, we never move backwards, always entering into uke's sphere of movement. Beginneres generally learn 4 basic irimi techniques.
1- Enter direct, you move your whole body as one keeping the forward foot forward, much like a "slide".
2-entering "off the line" . This is based on the theory that uke must at some time enter into your sphere to attack, we meet the attck by moving slightly off uke's center line but still are forward and now angled at uke's center. This is done to the inside of the attack.
3. Turning and entering. Still watching the attacker by keeping the head forward, the rest of the body turns to sideways (all turns start hip or center first), hands move from center to top of head, the hands reach the top of the sphere the body snaps back into a forward position and moving forward like in the first irimi.
4. Atemi, entering and turning. Atemi is a strike (This atemi is meant as a distraction rather than a damage infliction) As uke moves in for the attack, you step to the outside of the line of attack in horse stance (just like kungfu!) When sliding forward, the forward hand strikes at the attackers head, the strike is done in a circular motion so as to end up with uke's forward limb below that of the arm doing atemi, from the horse stance, you then snap back into basic stance with your hands extended. This is the basis for kokyo nage or breath throws (internal method)
Tenkan
Tenkan is turning on the forward foot. We put our weight on the ball of the foot and turn from the hips, this essential to 80% of all techniques. In judo there is pushing and pulling, in aikido it is "enter and turn". This is the blending many people hear about, we enter directly into an attackers space and then turn with their attackinenergy to effect a throw or lock.
Basic theory
The main point of aikido footwork is to maintain proper mai-ai or critical distance, thus controlling the "de-ai" the moment of "impact" for lack of a better word and to not get hit. Much like sword work, aikido tai sabaki (footwork also translated as techniques of body displacement) involves no hard blocks but rather parrys so as to continue the momentum of the attack. We try to very hard always maintain our center line and to upset that of the attackers.
You probably have more specific questions, so feel free to please ask. I can actually work out what ifs here at home with sensei.
Hope this was somewhat helpful.
bamboo