To unlock the keypad on your LG L38C mobile phone you need to first press the "Power/Lock" button, located on the top right of the handset. You then need to press the screen at the bottom and slide upwards, this will unlock the screen and give you access to the main screen - easy!
Here is a fun interactive website where you can go through the actions step by step to visualise exactly what I am talking about.
If you need any more help with your LG L38C, you can download an instructional manual here.
The phone comes installed with the Android operating system which is generally regarded as quite simple to use, but if this is the first time you have had a smartphone it can take a little while to get used to. AndroidCentral has a good "How To" section which is a great resource.