Combine two columns into one column in SQL and add it to existing table

How to merge or combine columns into one in SQL is shown

[vvkreddy]

Clear cut explanation, need more videos like this

[alexanderfeldman]

Concatenation will not take effect for new rows. How to alter table to apply concatenate two column values for new rows as well?

[Harikrishnan-nkjp]

how to change the position of newcolumn??? like what to do for the newcolumn to be in between name and salary??

[musicislost]

How would you do this but columns from different tables into 1 column