There are lots of ways to do this and bunches of unanswered questions.
LEDs drop about 2 to 3v, mostly depending on the color. (The drop is listed in the data sheet). They commonly have a current limit of 20 ma or 25 ma, unless they are high power types (again see the data sheet)
If you don't control the current they will be destroyed.
Commonly a string of LEDs in series is put in series with a resistor to limit the current and connected to a fixed voltage. For example: 5 LEDs that drop 2.1V connected in series drop 10.5V. If they are powered with 12V, a series resistor drops 12v-10.5v or 1.5v. By ohms law (not a local ordinance) E/I = R volts/current = resistance) or 1.5v / 20 mA = 1.5 / 0.02 = 75 so you need a 75 ohm resistor in series with each string of 5 LEDs. 120 LEDs would be laid out as 24 strings of LEDs, each wirh a resistor, all connected in parallel. At 20 mA this will draw 480 mA.
With a different voltage the calculations will be different. Simply rectifying AC with a filter capacitor results in about 170V. 76 LEDs that drop 2.1V will drop 160V so you need a series resistor that drops 10v at 20 ma or 500 ohms. The formula for power is P = E * I (watts = volts * amps). 10V at 20 mA (0.02A) dissipates 0.2W so you need at least a 1/4 watt resistor.
I would suggest the high side of all the LED strings be connected to +12V (in this example) and an N-ch mosfet connected with D (drain) connecting from the low sides of all the LED strings and S (source - of electrons) to ground. The mosfet can be powered (switched) by connecting a 5v microprocessor or timer IC to G (gate). If the micro has open collector outputs (pull to ground) a resistor, say 5kohm, to +V will be needed. The Nmosfet will be on When G is more than the NMosfet threshold above D -a few volts.
The mosfet must be sized to handle the current , but that's not hard. Mosfets have their on resistance listed on their datasheet along with power dissipation and you're back to ohms law and the formula for power to get the right size. Most TO-220 package will be way more than you need.
This is just the start. You need to control it somehow. There are gobs of choices. You will need a good understanding of basic electronics, algebra, and schematic symbols to get anywhere, unless you have someone do it all for you, and then what's the point. If it was easy everyone would do it.
You can find lots of help - tutorials, sample circuits, etc. on the web. You can also find lots of controller kits that would help. There are many and I haven't tried any, though Adafruit looks pretty good to me.
