How to work on Ubuntu without installing on PC ?

Target : To use ubuntu without installing it on PC.

Approach : Create a bootable USB stick and boot from it.

Assumption : Your PC already have Windows installed on it.

Steps

1. Download ubuntu

    Choose the flavor : 32 or 64 bit (64 bit recommended if PC has 2GB+ RAM) 

    It will give you an ISO file like, ubuntu-15.10-desktop-amd64.iso

2. Download USB installer from site Pen Drive Linux

    It will save file like, Universal-USB-Installer-1.9.6.2.exe

3. Plug in USB drive, which must have at least 2.5 GB free space

4. Open USB installer

    a. Select "ubuntu" as Linux distribution

    b. Select downloaded ubuntu ISO file (Disk image file)

    c. Choose USB drive and click Create

5. After creation of bootable USB, set your boot sequence in BIOS

    a. Restart PC, Goto BIOS by pressing F2/F8/F10 according to your PC model.

    b. Go to Boot sequence and set "External drive" as first boot preference.

    c. Restart PC so that it will boot by USB

    d. After boot choose the option : Try ubuntu without installating

Reference

http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-windows