Hello Amey,
I could not resist myself from adding a couple of lines here ..
1. A lot of informative stuff is already available on the subject. A good starting point can be SAP NetWeaver Gateway Self-Paced Learning - Technologies - SCN Wiki and Gateway Channel in Youtube.
2. Also a good resource that I personally find to be elaborate and effective is the recently released SAP Press book on Netweaver Gateway .
Of course you need to learn OData concepts first which is based on REST principle and language agnostic. In OData.org you get a lot of samples to start with. I have seen people picking up the OData concepts really very fast and I encourage you to give it a try.
Next is the OData modelling part - once you understand the OData concepts clearly, you can map ERP data to OData model. This requires little experience as the ERP data always can not be directly mapped to OData model. Gateway Offers eclipse based modeller tool as well as transaction SEGW for modelling. For simple cases there are tools and accelerators which will generate the model and service from data sources like RFC/BAPI/Genil/SPI/BW/External OData /Search Help. With a couple of clicks you get a running OData service exposing ERP data. In these cases knowledge on the relevant transactions is sufficient.
For more complex cases manual modelling knowledge helps. Most of the modelling can be done without any ABAP coding. However the data provisioning needs ABAP coding if your requirement is not met by the above mentions techniques. For complex data provisioning logic ABAP knowledge is a must.
The complexity varies based on the use case and scenario. I have seen customers creating excellent UI applications based on simple models whereas some other depend of complex OData service for specific use case.
And finally ... you need to understand the REST paradigm before you jump into development.
Give it a try, and I am sure you will find it easier than many other technologies. 
BR,
Atanu