Of course you can, but your code is incorrect.
You are declaring vel variable for velocity and in process function you are assigning a value to it, but you are not using it anywhere.
All Node2D’s functions and variables you can see on official documentation of Godot Engine: Node2D
I know what you want to do and I would write it this way:
extends Node2D
var speed = 100
var vel = Vector2()
func _ready():
set_process(true)
func _process(delta):
vel = Vector2() # set vel to Vector2(0, 0)
if Input.is_key_pressed(KEY_RIGHT): # detecting right key
vel = Vector2(speed, 0) # setting vel to desired direction
# Here would be code for KEY_UP, KEY_DOWN and KEY_LEFT
self.translate(vel * delta) # changing node's position