When should I take a test?

My last cycle was january 18th. I was supposed to start my period February fourteenth but a day before I started my period i am sure i have implantation bleeding anywho I was supposed to start monday i never started okay and todays tuesday I havent started yet anywho Im trying to see what kind of test can i buy where I can take it any part of the day and the results will be accurate. Also is your cervix supposed to be a certain way? I have heard low and high. Not for sure but mines is low right now what do you think I can do can anyone talk to me whether through email or instant messengar could you im me. Thanks and what brand of test should I buy?