I need clarification in two things

wha are the assumptions for a linear regression model?

and also

I need help with this image how can I interpreted? How do I know what does the "sig" column mean? and how do I Interpret the confidence intervals for the estimate of "60.84"

Coefficients" Unstandardized Standardized 95.0% Confidence Interval Coefficients Coefficients for B Model B SE Sig. Lower Bound Upper Bound (Constant] 60.84 .97 62.85 .000 58.933 62.747 GDP per 05 01 .54 9.90 .000 043 064 capita "Dependent variable: Life expectancy