They are simple present tense. They are examples that basic tense.
I play games now.
... is a very basic sentence. May be too basic and simple to be used in real life situations. Hardly anyone says it like that in real life.
I want a chocolate now.
... is also very basic. You may hear something like that in real life but saying it like that may make it sound like you're ordering someone to get you chocolate quite rudely.
They're grammatically correct but we usually don't say it like that. Instead, depending on the situation, we may say one of the following:
We're playing games now.
We'll be playing games now.
I'd like some chocolate.
I play games.
I want a chocolate.
Without the "now", these are perfectly fine sentences.
"I play games" actually means something like "I play games as a job/hobby", since the
simple present tense can be use to state something that is always true. If you want to say that you are playing games at that time, it's better to say "I'm playing games now".
"I want chocolate" itself expresses that the "wanting of some chocolate" is the the present. However, if "now" is added at the end and there is no prior context, it acts as an emphasis, which can be (mis)understood as "I want chocolate right now. Give me chocolate". If, however, you say "That was delicious. I want chocolate now.", that is perfectly fine and is actually used to mean something like "I want chocolate now because that was delicious".