I am currently working on an Arduino project and I need to buy a linear slide potentiometer. I am new to stuff like this and when I searched about these sliders, I found out that they come in different resistances. What does the resistance mean or refer to please?
That's the resistance between the two end terminals. Resistance between a given end terminal and the wiper will be between 0 and that resistance depending on it's position.
It determines the amount of current that will continually flow. Higher values mean less current. A 10K ohm pot will have 0.5 mA flow at all times at 5 V, which is probably a pretty good value, though it is not critical.
Bourns makes some nice slide pots, linear and audio taper, single and dual, manual and motorized.
Here are a bunch of 10K pots
I used some of these in a current project, PTB6044-2010BPA103-ND.
Had to actually buy one to understand the hole placement and sizing, the datasheet is a bit unclear as to which are the mechanical hold in place parts and which are the signal pins.
What are you doing with the slide pots?
If you are just using them as inputs to Arduino then any reasonable value from 2K to 20K or more is fine. You are just using them as voltage dividers to send signals to Arduino.
IF you are using the pots as part of some other electronics device, then the considerations are different.
Some info HERE.