You can find the gender of a guppy by looking at the anal fin. The anal fin is the closest fin to their tail below them. On a female it will look like a normal fin but on the male their will be 2 long skinny fins. The male is also much more colorful.
All that is needed is a male guppy in with her.
No.
Female guppies are larger and plainer. The male is distinctive for his long, flowing, colourful tail and generally brilliant colours.
If the fish has a "GONOPODIUM" it is definitely a male.
The Gravid female will have the dark "gravid spot" in front of her vent. I can however assure you that if there has been a male in the same tank with a female guppy for any reasonable length of time she will be gravid.
No, unless a) the female fish got pregnant before the male died, or b) you buy a new male guppy and put him in with the female.
It might want to mate with it.
Your male guppy is female and with child.
yes there are. that is how they get mates.
A male guppy will fertilise any female guppy it is in with. Mother,sister, no relation, whatever. It doesn't know and it doesn't care. That is nature.
Yes, you must have a male and female to breed.
A female or male goldfish can be any colour. The colour of the fish does not determine the sex of the fish.