Consider titrating an unknown chloride sample with 0.10 +/- 0.01M AgNO3 and the following data:

Initial Buret reading-0.19 +/- 0.02mL
Final Buret reading- 9.26 +/- 0.03mL
Unknown sample mass- 95.0 +/- 0.2mg

Find the weight 5 of Cl- in the sample.

These things are difficult to do on the web but here is the process.

9.26 +/- 0.02
-.19 +/- 0.03
-------------
9.07 +/-(?)
? = sqrt[(0.02^2) + (0.03)^2)]
? = 0.036 and that difference is displayed as
9.07 +/- 0.036

Then you go to the mass and % by mass.
[9.07 (+/- 0.036) x 0.1M (+/- 0.01) x 143.34]/95.0 )+/- 0.2) and all of that x 100 to convert to %.
Do te same kind of thing but this time with the two multiplications and division.
I can try to answer specific questions but i urge you to look in your text/notes for this topic.