Codigo.

Create:
hsp = 0; //velocidade horizontal
vsp = 0; //velocidade vertical
grv = 0.4; //gravidade
walksp = 3; //velocidade do personagem

Step:
//get player input
key_left = keyboard_check(vk_left);
key_righ = keyboard_check(vk_right);
key_jump = keyboard_check_pressed(vk_space);

//calculate movement
var move = key_righ - key_left;
hsp = move * walksp;
vsp = vsp + grv;
if (place_meeting(x,y+1,oWall)) && (key_jump)
{
    vsp = -7;
}

//horizontal collision
if (place_meeting(x+hsp,y,oWall))
{
    while (!place_meeting(x+sign(hsp),y,oWall))
        {
            x=x+sign(hsp);
        }
    hsp = 0;
}
x=x+hsp;

//horizontal collision
if (place_meeting(x+hsp,y,oWall))
{
    while (!place_meeting(x+sign(hsp),y,oWall))
        {
            x=x+sign(hsp);
        }
    hsp = 0;
}
x=x+hsp;

//vertical collision
if (place_meeting(x,y+vsp,oWall))
{
    while (!place_meeting(x,y+sign(vsp),oWall))
        {
            y=y+sign(vsp);
        }
    vsp = 0;
}
y=y+vsp;

//aqui ficam as animações:
//Animation
if (!place_meeting(x,y+1,oWall))
{
    sprite_index= sPlayerA;
    image_speed= 0;
    if (sign(vsp)>0) image_index= 1; else image_index= 0;
}
else
{
    image_speed= 1;
    if(hsp==0)
    {
        sprite_index=sPlayer;
    }
    else
    {
        sprite_index=sPlayerR;
    }

}
//fazer o sprite do personagem virar ao mudar a direção esquerda ou direita
if(hsp != 0) image_xscale=sign(hsp);