Dear Viraj
Hope, this helps.
IT (Information Technology) is a catch-all for the industry at present, any job that is primarily to do with the operation of computers or developing for them is within the "IT industry/sector".

However, within the UK at least, job descriptions and adverts tend to reserve "IT" within a jobtitle, as administration, procurement and technical support for company computing resources. Everything from sysadmin work, to frontline technical support, or hardware repair and procurement/policy for internal IT.

Software Engineering specifically means developing software, analysis, design, programming - creating new software, or maintaining/altering existing software. This is very different to a technical role. The skill set is quite different, technical support guys are not necessarily programmers and (contrary to a lot of non-IT peoples' belief structures) software engineers are not necessarily any good at technical support. Though Software Engineers are within the "IT sector", which confuses the matter slightly in the job market.

Yes they both are different branches.