Sublist3r - Tutorial
Sublist3r is a python based tool which is designed to enumerate subdomains of websites using OSINT. It comes in handy for penetesters and bug bounty hunters to collect and gather subdomains for the domain they are targeting.

It enumerates subdomains using many search engines such as Google, Yahoo, Bing, Baidu and Ask. Sublist3r also enumerates subdomains using Netcraft, Virustotal, ThreatCrowd, DNSdumpster and ReverseDNS.
So how to install it ?
Commands:
1) git clone https://github.com/aboul3la/Sublist3r.git
2) cd Sublist3r
3) sudo pip install -r requirements.txt
After installing any tool always check the "--help"
python sublist3r.py -h

Now to run the tool against any target you can use the command
python sublist3r.py -d <target-domain>
To save the output into a text file you can use command
python sublist3r.py -d <target-domain> -o <filename>.txt
if you face any difficulties then do let us know in the comment section