Can I summon a lvl. 1-4 monster from my hand on my first turn?
Yes you can, however in yugioh you will refer to the stars as levels which go from the right hand side of the card, and with XYZ monsters the stars are known as ranks which go from the left of the card.

Further description on summoning:

In yugioh there are what is known as normal summons and special summons. Special summons usually (special summoning from the extra deck doesn't always come from a card effect) occur via card effects and usually state what kind of monster that effect can special summon for example the card ancient rules


  Special Summon 1 Level 5 or higher Normal Monster from your hand.


This effect states the type of monster it can summon (being a level 5 or higher normal monster)

You can special summon monsters as many times as you want per turn 

For normal summons this is a bit trickier, you can only conduct one normal summon per turn unless you have a card that allows you to make more normal summons like double summon


  You can conduct 2 Normal Summons/Sets this turn, not just 1.


With a normal summon you can summon a level 1-4 monster straight away however you to summon a level 5 or higher monster you must first tribute (send to the graveyard) monster(s) already on your field. Level 5 and 6 monsters require you to tribute one preexisting monster on the field and level 7 or higher monsters require 2 preexisting monsters on the field unless the monster states in its card text otherwise like Obelisk the Tormentor emphasis mine


  Requires 3 Tributes to Normal Summon (cannot be Normal Set). This card's Normal Summon cannot be negated. When Normal Summoned, cards and effects cannot be activated. Cannot be targeted by Spells, Traps, or card effects. Once per turn, during the End Phase, if this card was Special Summoned: Send it to the Graveyard. You can Tribute 2 monsters; destroy all monsters your opponent controls. This card cannot declare an attack the turn this effect is activated.


These are what is known as a tribute summon. Tribute summons are a type of normal summon so they do count as your one normal summon for the turn.

You can find more information about summoning in the rule book on page 18.