How do I concatenate strings in a bash script?

Nothing special, you just need to add them to your declaration.
For example:

stringOne="foo"
stringTwo="anythingButBar"
stringThree=$stringOne$stringTwo
echo $stringThree

fooanythingButBar

if you want the literal word 'and' between them:

stringOne="foo"
stringTwo="anythingButBar"
stringThree="$stringOne and $stringTwo"
echo $stringThree

foo and anythingButBar

If instead you had:

stringOne="foo"
stringTwo="anythingButBar"
stringThree="%s and %s"

you could do:

$ printf "$stringThree\n" "$stringOne" "$stringTwo"
foo and anythingButBar

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