"Star notes" are bills printed to replace others that were damaged during the printing process. However a date is needed; please post a new question with that information.
The serial number on a dollar bill and other currency refers to the note series, and the Federal Reserve bank that issued the note. The serial number is used to keep track of currency.
All $2 Federal Reserve Notes are worth only face value if circulated, $2.50 to $3.00 uncirculated.
Between $10 - $20 unless the serial number ends with a star.
The condition and serial number are important. But most likely around $25.
A 1934 A green seal one hundred dollar bill is only worth face value unless it is in perfect mint condition. If it has a star following the serial number, it could be worth up to $200 depending on the serial number and condition.
It is likely just worth $100. Being in perfect condition or having a serial number with a star symbol at the end of it can add value.
$20 Federal Reserve Notes have been issued for over a century so more information is needed. Please post a new, separate question with the bill's date and what letter, if any, is next to the date. You don't need to include the serial number, though.
If you check the bills in your wallet you'll see that nearly all of them have different letters at the start and end of their serial number. The first letter on a $1 bill indicates the Federal Reserve District for which the bill was printed - it should match the letter in the center of the Federal Reserve seal. The other letter is just sequential, to provide 26 times more possible serial numbers than could be created with only 8 digits.
$100
The issuing district on a twenty dollar bill can be found by looking at the first letter of the serial number on the bill. Different letters correspond to different Federal Reserve Banks, which are located in various cities across the United States.
To identify if a 1976 two dollar bill is from Kansas, you can check the serial number. If the bill's serial number starts with the letter "K," it signifies that the bill was printed in the Kansas City, Missouri, facility.
The star at the end of the serial number signifies that the original note did not meet Federal printing standards and was replaced with that note.