The novice accepted the deal before he had a chance to check his finances, which put him in a state of conflict when he realized he had a straight flush.

Can anyone explain the meaning of the above sentence in simple English?
Is it about poker? Deal - the cards dealt to him by the dealer

his finances - how much money he had left for gambling

straight flush - an extremely good hand!
Yes; maybe: "the novice accepted the proposal before he had had a chance to check how much money he could invest in it; which caused problems when he realized it was a very good proposal, in which he would have liked to invest a large amount of money".