As a goblin, you are small and agile, as well as for some reason thicker skinned and able to resist powerful impacts better. Because of this you get a +2 to DEX and +1 to CON. Reasons for DEX are because you are small and nimble, as for CON it's because the goblins in this world can for some reason tank more damage than normal.

As a goblin you are able to manipulate simple weapons with ease as it was necessary for your species survival, and studded leather armor provided protection for your species when they were more looked down on. So you get proficiencies in those categories.

Goblins have the capability to perform sneak attacks very well but since sneak attack is a Rogue-specific action goblins have dark vision instead. Can see objects up to 60ft in the dark as if the area were well lit instead. Passive ability.

Since goblins are small and picked on a lot, the deities decided to give goblins a little extra oomph whenever you land a hit. Scales off your character level, so if you're Level 1 you deal 1 extra damage, if you're Level 2 you deal 2 extra damage and so on, in a linear fashion.

As a goblin since you're so tiny and agile you can take a bonus action to disengage from the enemy or hide in a corner making it harder for the enemy to notice you. Can only be done at the end of each turn but there's no cooldown.