The procedure for making a custom walk animation using the Geckolib plugin

Firstly, the procedure should be placed in the entity tick trigger.

It should look like:

Event Trigger (the top green part) [no additional trigger]

IF {[X velocity not equal to 0] AND [Z velocity not equal to 0]} OR {[X velocity not equal to 0] OR [Z velocity not equal to 0]}

   do IF [Get Event/target entity] data logic NBT tag "PlayingAnim" = false

     do {Play animation [animationnamehere] as entity [Event/target entity]. Should loop = false}

       Set [Event/target entity] data logic NBT tag "PlayingAnim" to true

    Else {set [Event/target entity] data number NBT tag "AnimTimer" to [Get [Event/target entity] data number NBT tag "AnimTimer"] - [1]

       IF [Get [Event/target entity] data number NBT tag "AnimTimer"] is less than or equal to [0]

         do {Set [Event/target entity] data logic NBT tag "PlayingAnim" to false}

              {Set [Event/target entity] data number NBT tag "PlayingAnim" to [animation time in seconds *20]}

Else if {[X velocity = 0] AND [Z velocity = 0]}

         do {Set [Event/target entity] data logic NBT tag "PlayingAnim" to false}

              {Set [Event/target entity] data number NBT tag "PlayingAnim" to [animation time in seconds *20]}

LMK if you have questions!