( Basically ( , ( it ( ( 's ( satellites ( ( sent up ) ( into ( ( space , ) ( that ( ( ( ( using ( ( ( at least ) 4 ) ( of ( these satellites ) ) ) ) ( , ( can ( ( pinpoint ( your ( specific position ) ) ) ( on ( ( the surface ) ( of ( the earth ) ) ) ) ) ) ) ) or ) ( slightly ( above it ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB Basically)) (, ,) (NP (PRP it)) (VP (VBZ 's) (NP (NP (NNS satellites)) (VP (VBN sent) (PRT (RP up)) (PP (IN into) (NP (NP (NN space)) (, ,) (SBAR (WHNP (WDT that)) (S (VP (VP (S (VP (VBG using) (NP (NP (QP (IN at) (JJS least) (CD 4))) (PP (IN of) (NP (DT these) (NNS satellites)))))) (, ,) (MD can) (VP (VB pinpoint) (NP (PRP$ your) (JJ specific) (NN position)) (PP (IN on) (NP (NP (DT the) (NN surface)) (PP (IN of) (NP (DT the) (NN earth))))))) (CC or) (VP (ADVP (RB slightly)) (PP (IN above) (NP (PRP it)))))))))))) (. .)))
Basically, it's satellites sent up into space, that using at least 4 of these satellites, can pinpoint your specific position on the surface of the earth or slightly above it.
(ROOT (S (NP (NNS Satellites)) (VP (VBP are) (NP (NP (JJ man-made) (NNS devices)) (PP (IN in) (NP (NN space))) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (VP (VBN used) (S (VP (TO to) (VP (VB observe) (NP (NP (DT the) (NN earth) (POS 's)) (NN surface))))))))))) (. .)))