The lowest frequency!

You should use the same speed as the sampling rate(Fs) of your input signal.

Your cutoff point is then related to that Fs. For example if a lowpass filter cutoff is 0.25Fs and your signal rate is 12MHz then the cutoff will be 3MHz meaning all frequencies from 0 to 3MHz are passed.

your frequency may be labelled in terms of Fs ratio or in radians(0 ~ pi) where pi means .5Fs

For more advanced designers, you can pass your input signal to a higher or lower data rate(interpolation/decimation)

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but i try whith sample rate 10MHz and filter type is bandpass have cutoff are 200Hz and 300Hz

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That's not impossible in theory, but practically, cause you would require several thousand FIR taps in this case. Just consider, that the filter must have at least a length equivalent to several periods of the characteristic filter frequencies. You can either build IIR filters, although they need a rather large coeffecient length and a lot of extra fractional bits, but they are basically feasible for such extreme frequency ratios. Or use a decimation before the filter.