I know the rules of the game, but for some reason sacrificing monsters is not a possibility from my end. How do you go about sacrificing monsters on this game? I know for a monster with 5 stars I have to sacrifice 1 monster, and for a monster with 7 stars, it requires 2 monsters. Please help so I can actually play my monsters. (Sorry if I sound like a complete amateur, I just really cannot grasp the online version of the game.)

It's quite simple actually. If you have grasped the concept of summoning low level monster than you are golden. Summoning Higher Level Monsters is done exactly the same.

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It's quite simple actually. If you have grasped the concept of summoning low level monster than you are golden. Summoning Higher Level Monsters is done exactly the same.

Yes, I understand the concept, the problem is when I try to play a card, say The Dark Magician, it won't give me the option to sacrifice any monsters whether they are on the field or in my hand.

could you give me a screenshot or a replay for the situation?

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First, you can only 'tribute' (the official word) monsters on the field.
Second, remember you can only Normal Summon once per turn. So if you just Normal Summoned a monster, you can't try to summon your Dark Magician in the same turn, you have to wait till next turn.

Assuming you do everything right, you should be able to click on Dark Magician, then on "Normal Summon", then you would get a prompt that this will require 2 tributes, and then the monsters on the field should light up, and you will be able to click on them to 'mark' them for tributing.