MySQL help

I'm having trouble figuring out how to use SQL to select when there are multiple levels of keys that link tables together.

For example, look at the following table structure in a database:

tblUserDepartments
field: deptID
field: userID

tblUserInfo
field: userID
field: userName
field: activityID

tblActivityPlan
field: activityID
field: activityName
field: plannedCount
field: actualCount

Now, I want to specify a deptID, and have it find each user that is in that department, and then find each activity plan for each user, and then create a record for each distinct activity...showing the planned and actual count for those activities.

Example desired recordset output:

UserName | ActivityName | Planned Count | Actual Count
Joe Smith | Social Work | 4 | 2
Joe Smith | Other Work | 3 | 3
Margaret R | Freel Work | 5 | 6

I don't see how I can use the general SQL queries when there are multiple levels of selecting necessary like this.

I could start with something like:

SELECT userID INTO tempUsers
FROM tblUserDepartments
WHERE tblUserDepartments.deptID = MyDeptID

SELECT userName, activityID INTO tempActivities
FROM tblUserInfo
WHERE tblUserInfo.userID = tempUsers.userID

SELECT activityName, plannedCount, actualCount
FROM tblActivityPlan
WHERE tblActivityPlan.activityID = tempActivities.activityID

I'm starting to confuse myself...this isn't right. I am thinking that somehow I should be using JOIN.