This may seem like a lot but keep in mind that you don’t use classes or weapons, really, do this is essentially how you use the world. Each morph will level at different rates and with feats you can accelerate that.
Unless specifically stated every acquired morph is Level One.
When you level in your natural form all your morphs go up one level. That means if you acquire a Tiger at level one and a Tortoise at level five, your tiger will always be a higher level than your tortoise–unless you use feats.
Level One
HP Proficiency Bonus +1 1 Attack
Most of this information will be on your morph card. You do not add anything to your HP at level one. You get 1 attack in combat. Your proficiency bonus is +1.
Level Two
HP Proficiency Bonus +1 1 Attack
When leveling up you add the morphs HP per level. It’s always at max no need to roll any die. However you do not add any CON to your HP. There are feats that will let you additionally increase the HP but without them you just add the HP per level number.
Level Three
HP 1D4 Skills Proficiency Bonus +1 1 Attack
Your morph gets skills too and those are listed as proficiencies on your morph card. At level three you get to roll 1D4, you have that many points to add to those skills. Each point equals an additional +1 bonus to your chosen skill. You may dump them all into one skill or spread them out.
Level Four
HP Stat By 1 or Feat Proficiency Bonus +1 1 Attack
At level four you have the option to increase a Stat by one (STR, CON or DEX) or take a Feat.
Level Five
HP Proficiency Bonus +2 1 Attack
At level five your morph’s proficiency bonus goes up. This does not mean you add +3 to your rolls, it means the total is now +2.
Level Ten
HP Proficiency Bonus +3 2 Attacks
At level ten you get your first attack increase. This means your level ten morph may now make two attacks in a round of combat instead of one attack.