You can join the Railways in the following ways as an engineer-
1. Railway Recruitment Board (RRB) Exam
2. IES exam conducted by UPSC
The jobs offered after clearing RRB are-
Section Research Engineer
Depot Material Superintendent
Junior Research Engineer
The jobs offered after clearing IES are as follows-
Indian Railway Service of Engineers
Indian Railway Stores Services
To check the eligibility do check their websites on a regular basis.
Hope this helped!