How to concatenate two strings or several strings into one string in B-shell?

Shell Programming and Scripting
1

like connect "summer" and "winter" to "summerwinter"?
Can anybody help me? thanks a lot.

2 
#!/bin/sh

season1='summer'
season2='winter'

echo "[${season1}] + [${season2}] = [${season1}${season2}]"
3

it works great.