几个函数不明白

procedure TForm1.Button1Click(Sender: TObject);
var
picture2:tpicture;
begin
if openpicturedialog2.FileName='' then
begin
showmessage('请选择照片');
exit;
end;
if snedit1.Text='' then
begin
showmessage('请输入用户名!');
exit;
end;
picture2:=tpicture.create;
picture2.LoadFromFile(extractfilename(openpicturedialog2.FileName));
adoquery2.Close;
adoquery2.SQL.Clear;
adoquery2.SQL.Add('select*from base_data');
adoquery2.Open;
adoquery2.Insert;
adoquery2.FieldByName('worker_id').AsString:=snedit1.Text;
adoquery2.FieldByName('photo').Assign(picture2);
adoquery2.Post;
showmessage('图片已保存完毕');
end;
我对以上几个函数不太清楚！
1、extractfilename？
2、Assign？
3、post?
谢！