I always love your questions Pelin - where are you finding these?
To be "small-time" means to be insignificant or very small in power and experience.
For example: "You've only just started in this company. In comparison to him, you're small-time!"
Another way to say the same sentence would be: "In comparison to him, you have no experience or power in this workplace yet".
The opposite, is "big-time".
For example: "Wow, he is so good at basketball, he could make it big-time!!"
I hope that helps you Pelin.