3V to 5V DC DC Converter

You can Google the same and you will find a lot of circuit diagrams for 3 to 5V DC-DC converter. If you are already following a schematic and you are facing any problem in that, please share the exact problem with details of your schematics

Easiest solution is to buy a 3-5v volt boost converter module, its very cheap around INR 150.

Otherwise there are many ICs available for that purpose. One of the popular IC is MC34063, which has capability to output  maximum of 40v and1.5A current. Input voltage can be in between 3v-40v. Output voltage is adjustable depending upon the external components used in circuit. 

Also you didn't mention the current requirement of your circuit.

The circuit that you are asking for is called a Boost converter. As Maddy has suggested you can use the MC34063 IC to build your circuit. The circuit diagram for the same is given below

If you want to understand how the circuit works you can read about the 3.7V to 5V Boost converter Tutorial here. 

Now coming to your second question "What is the difference between a Voltage Regulator and a DC-DC converter (Chopper)"?

A chopper is a general term used to define all the voltage converter circuits where a power electronics switch like a MOSFET or IGBT is involved. For example the Buck converter, Boost converters, SMPS circuits everything falls under the term choppers. A chopper is device that converts Fixed DC input Voltage to a Variable DC output voltage like the RPS in your Lab. Here the Output coltage can either be greater or less than the input voltage.

A Voltage regulator in the other hand is just the opposite to chopper it is used to provide constant DC output voltage from a variable DC input voltage. It does not involved any power electronic switches like FET or IGBTs. For example if you are powering your circuit with 12V and your circuit needs 5V to operate then you will use a voltage regulator circuit (like a 7805) to convert the 12V from battery into 5V for your circuit. Here the input voltage will be always greater than output voltage.

Due to the operating principle Voltage Regulators are always less efficient than choppers