This way you can create a small navigation of content elements. If there is no item selected in the menu all contents are displayed. When you select an item on the content navigation, only that item is displayed:

temp.contentnav = CONTENT
temp.contentnav {
  table = tt_content
  select {
    pidInList = this
    orderBy = sorting
    where = colPos=0
    languageField=sys_language_uid
     
  }
  renderObj = TEXT
  renderObj {
    field = header 
    wrap=<span class="text">|</span><br>
    typolink.parameter.field=pid
    typolink.parameter.dataWrap=|
    typolink.additionalParams.insertData=1
    typolink.additionalParams=&content_id={field:uid}
    typolink.no_cache=1
    if.isTrue.field=header
  }
   
   
}
page.10.subparts.CONTENTNAV < temp.contentnav

And this is the code, to show only the selected content element...

page.10.subparts.CONTENT>
page.10.subparts.CONTENT=CONTENT
page.10.subparts.CONTENT {
  table=tt_content
  select{
    andWhere.insertData=1
    andWhere=uid={GPvar:content_id}
    andWhere.if.isTrue.data=GPvar:content_id
  }
}

Click here to see what it looks like