How to get an output of SHA-1 with first 2-bit are zeros? Can someone explain what are the ways to get an output of SHA-1 with first 2-bits which are zeros?
Hash random values until you get a hash with two leading zeroes. We would expect  about 1 in 4 values to have a hash-value of that form.
So let's try this:
echo hello | sha1sum
f572d396fae9206628714fb2ce00f72e94f2258f  -

Nope.
echo hello1 | sha1sum
0ef562ff2d0c21358f9d289f1c908436714fc923  -

There we are, 4 leading zeroes.