You perform a regular poke attack by walking into an enemy with your sword held out. This deals half as much damage as a normal slash or dash attack with any of the L2-L4 swords. The Fighter's Sword is so weak, that both the poke and slash attacks deal the minimum (= the same) amount of damage. If you have the Pegasus Boots, you can get Link to keep his sword held out after the attack by partially charging a dash just after connecting with the enemy.
A pokedash is performed by charging a dash (pre-emptively) the moment you are connecting with the enemy. This makes the poke deal the damage of a full dash attack, i.e. twice as much as a normal poke. If you hold the charge for long enough after the attack, you can keep the sword held out and keep on repeating pokedashes (and potentially end the combo with a spin attack once the sword is fully charged). Note that while you are holding down, your sword charge timer will be suspended and it will take respectively longer to fully charge a spin attack.