bash script order of execution

Do lines in a bash script execute sequentially? I can't see any reason why not, but I am really new to bash scripting and I have a couple commands that need to execute in order.

For example:

#!/bin/sh
# will this get finished before the next command starts?
./someLongCommand1 arg1
./someLongCommand2 arg1

Yes, they are executed sequentially. However, if you run a program in the background, the next command in your script is executed immediately after the backgrounded command is started.

#!/bin/sh
# will this get finished before the next command starts?
./someLongCommand1 arg1 &
./someLongCommand2 arg1 &

would result in an near-instant completion of the script; however, the commands started in it will not have completed. (You start a command in the background by putting an ampersand (&) behind the name.

Yes... unless you go out of your way to run one of the commands in the background, one will finish before the next one starts.